Instruct: Given a scientific claim, retrieve relevant passages that support or refute the claim.
Query: Ethanol stress increases the expression of PSP in bacteria.
Understanding the genetic basis of adaptation is a central problem in biology. However, revealing the underlying molecular mechanisms has been challenging as changes in fitness may result from perturbations to many pathways, any of which may contribute relatively little. We have developed a combined experimental/computational framework to address this problem and used it to understand the genetic basis of ethanol tolerance in Escherichia coli. We used fitness profiling to measure the consequences of single-locus perturbations in the context of ethanol exposure. A module-level computational analysis was then used to reveal the organization of the contributing loci into cellular processes and regulatory pathways (e.g. osmoregulation and cell-wall biogenesis) whose modifications significantly affect ethanol tolerance. Strikingly, we discovered that a dominant component of adaptation involves metabolic rewiring that boosts intracellular ethanol degradation and assimilation. Through phenotypic and metabolomic analysis of laboratory-evolved ethanol-tolerant strains, we investigated naturally accessible pathways of ethanol tolerance. Remarkably, these laboratory-evolved strains, by and large, follow the same adaptive paths as inferred from our coarse-grained search of the fitness landscape.
The effects of a set of stress treatments on gene expression of Chironomus thummi salivary gland cells have been analyzed. Among the treatments assayed, only during recovery from carbon dioxide have we observed a response similar to that previously described after heat-shock treatment: induction of the heat-shock puffs and synthesis of the heat-shock polypeptides. In these conditions, puffing and transcription of telomeric regions were observed, which led to the appearance of the temperature-inducible telomeric Balbiani ring T-BR-III. Other treatments failed to induce the heat-shock response, despite promoting real stress conditions to C. thummi larvae or salivary gland cells.
The bacterial type VI secretion system (T6SS) is a dynamic organelle that bacteria use to target prey cells for inhibition via translocation of effector proteins. Time-lapse fluorescence microscopy has documented striking dynamics of opposed T6SS organelles in adjacent sister cells of Pseudomonas aeruginosa. Such cell-cell interactions have been termed "T6SS dueling" and likely reflect a biological process that is driven by T6SS antibacterial attack. Here, we show that T6SS dueling behavior strongly influences the ability of P. aeruginosa to prey upon heterologous bacterial species. We show that, in the case of P. aeruginosa, T6SS-dependent killing of either Vibrio cholerae or Acinetobacter baylyi is greatly stimulated by T6SS activity occurring in those prey species. Our data suggest that, in P. aeruginosa, T6SS organelle assembly and lethal counterattack are regulated by a signal that corresponds to the point of attack of the T6SS apparatus elaborated by a second aggressive T6SS(+) bacterial cell. PAPERFLICK:
BACKGROUND & AIMS Although the p53 tumor suppressor has been extensively studied, many critical questions remain unanswered about the biological functions of p53 homologs, p73 and p63. Accumulating evidence suggests that both p73 and p63 play important roles in regulation of apoptosis, cell differentiation, and therapeutic drug sensitivity. METHODS Gastric epithelial cells were cocultured with Helicobacter pylori, and the roles of p63 and p73 proteins were assessed by luciferase reporter, real-time polymerase chain reaction, immunoblotting, and cell survival assays. Short hairpin RNA and dominant-negative mutants were used to inhibit activity of p73 and p63 isoforms. Human and murine gastric tissues were analyzed by immunohistochemistry with p73 and p63 antibodies and modified Steiner's silver method. RESULTS Interaction of H pylori with gastric epithelial cells leads to robust up-regulation of p73 protein in vitro and in vivo in human gastritis specimens and H pylori-infected mice. The p73 increase resulted in up-regulation of pro-apoptotic genes, NOXA, PUMA, and FAS receptor in gastric epithelial cells. Down-regulation of p73 activity suppressed cell death and Fas receptor induced by H pylori. Bacterial virulence factors within the cag pathogenicity island, c-Abl tyrosine kinase, and interaction with p63 isoforms control the activity of p73. CONCLUSION Our findings implicate p73 in H pylori-induced apoptosis and more generally suggest that the p53 family may play a role in the epithelial cell response to H pylori infection.
The type VI secretion system (T6SS) is the most prevalent bacterial secretion system and an important virulence mechanism utilized by Gram-negative bacteria, either to target eukaryotic cells or to combat other microbes. The components show much variability, but some appear essential for the function, and two homologues, denoted VipA and VipB in Vibrio cholerae, have been identified in all T6SSs described so far. Secretion is dependent on binding of an α-helical region of VipA to VipB, and in the absence of this binding, both components are degraded within minutes and secretion is ceased. The aim of the study was to investigate if this interaction could be blocked, and we hypothesized that such inhibition would lead to abrogation of T6S. A library of 9,600 small-molecule compounds was screened for their ability to block the binding of VipA-VipB in a bacterial two-hybrid system (B2H). After excluding compounds that showed cytotoxicity toward eukaryotic cells, that inhibited growth of Vibrio, or that inhibited an unrelated B2H interaction, 34 compounds were further investigated for effects on the T6SS-dependent secretion of hemolysin-coregulated protein (Hcp) or of phospholipase A1 activity. Two compounds, KS100 and KS200, showed intermediate or strong effects in both assays. Analogues were obtained, and compounds with potent inhibitory effects in the assays and desirable physicochemical properties as predicted by in silico analysis were identified. Since the compounds specifically target a virulence mechanism without affecting bacterial replication, they have the potential to mitigate the virulence with minimal risk for development of resistance.
Bacteria encode a single-stranded DNA (ssDNA) binding protein (SSB) crucial for genome maintenance. In Bacillus subtilis and Streptococcus pneumoniae, an alternative SSB, SsbB, is expressed uniquely during competence for genetic transformation, but its precise role has been disappointingly obscure. Here, we report our investigations involving comparison of a null mutant (ssbB(-)) and a C-ter truncation (ssbBΔ7) of SsbB of S. pneumoniae, the latter constructed because SSBs' acidic tail has emerged as a key site for interactions with partner proteins. We provide evidence that SsbB directly protects internalized ssDNA. We show that SsbB is highly abundant, potentially allowing the binding of ~1.15 Mb ssDNA (half a genome equivalent); that it participates in the processing of ssDNA into recombinants; and that, at high DNA concentration, it is of crucial importance for chromosomal transformation whilst antagonizing plasmid transformation. While the latter observation explains a long-standing observation that plasmid transformation is very inefficient in S. pneumoniae (compared to chromosomal transformation), the former supports our previous suggestion that SsbB creates a reservoir of ssDNA, allowing successive recombination cycles. SsbBΔ7 fulfils the reservoir function, suggesting that SsbB C-ter is not necessary for processing protein(s) to access stored ssDNA. We propose that the evolutionary raison d'être of SsbB and its abundance is maintenance of this reservoir, which contributes to the genetic plasticity of S. pneumoniae by increasing the likelihood of multiple transformation events in the same cell.
Nociceptor sensory neurons are specialized to detect potentially damaging stimuli, protecting the organism by initiating the sensation of pain and eliciting defensive behaviours. Bacterial infections produce pain by unknown molecular mechanisms, although they are presumed to be secondary to immune activation. Here we demonstrate that bacteria directly activate nociceptors, and that the immune response mediated through TLR2, MyD88, T cells, B cells, and neutrophils and monocytes is not necessary for Staphylococcus aureus-induced pain in mice. Mechanical and thermal hyperalgesia in mice is correlated with live bacterial load rather than tissue swelling or immune activation. Bacteria induce calcium flux and action potentials in nociceptor neurons, in part via bacterial N-formylated peptides and the pore-forming toxin α-haemolysin, through distinct mechanisms. Specific ablation of Nav1.8-lineage neurons, which include nociceptors, abrogated pain during bacterial infection, but concurrently increased local immune infiltration and lymphadenopathy of the draining lymph node. Thus, bacterial pathogens produce pain by directly activating sensory neurons that modulate inflammation, an unsuspected role for the nervous system in host-pathogen interactions.
Horizontal gene transfer (HGT) in bacteria and archaea occurs through phage transduction, transformation, or conjugation, and the latter is particularly important for the spread of antibiotic resistance. Clustered, regularly interspaced, short palindromic repeat (CRISPR) loci confer sequence-directed immunity against phages. A clinical isolate of Staphylococcus epidermidis harbors a CRISPR spacer that matches the nickase gene present in nearly all staphylococcal conjugative plasmids. Here we show that CRISPR interference prevents conjugation and plasmid transformation in S. epidermidis. Insertion of a self-splicing intron into nickase blocks interference despite the reconstitution of the target sequence in the spliced mRNA, which indicates that the interference machinery targets DNA directly. We conclude that CRISPR loci counteract multiple routes of HGT and can limit the spread of antibiotic resistance in pathogenic bacteria.
Stressed cells coordinate a multi-faceted response spanning many levels of physiology. Yet knowledge of the complete stress-activated regulatory network as well as design principles for signal integration remains incomplete. We developed an experimental and computational approach to integrate available protein interaction data with gene fitness contributions, mutant transcriptome profiles, and phospho-proteome changes in cells responding to salt stress, to infer the salt-responsive signaling network in yeast. The inferred subnetwork presented many novel predictions by implicating new regulators, uncovering unrecognized crosstalk between known pathways, and pointing to previously unknown 'hubs' of signal integration. We exploited these predictions to show that Cdc14 phosphatase is a central hub in the network and that modification of RNA polymerase II coordinates induction of stress-defense genes with reduction of growth-related transcripts. We find that the orthologous human network is enriched for cancer-causing genes, underscoring the importance of the subnetwork's predictions in understanding stress biology.
Bacterial pathogens produce complex carbohydrate capsules to protect against bactericidal immune molecules. Paradoxically, the pneumococcal capsule sensitizes the bacterium to antimicrobial peptides found on epithelial surfaces. Here we show that upon interaction with antimicrobial peptides, encapsulated pneumococci survive by removing capsule from the cell surface within minutes in a process dependent on the suicidal amidase autolysin LytA. In contrast to classical bacterial autolysis, during capsule shedding, LytA promotes bacterial survival and is dispersed circumferentially around the cell. However, both autolysis and capsule shedding depend on the cell wall hydrolytic activity of LytA. Capsule shedding drastically increases invasion of epithelial cells and is the main pathway by which pneumococci reduce surface bound capsule during early acute lung infection of mice. The previously unrecognized role of LytA in removing capsule to combat antimicrobial peptides may explain why nearly all clinical isolates of pneumococci conserve this enzyme despite the lethal selective pressure of antibiotics.
Expression of particular drug transporters in response to antibiotic pressure is a critical element in the development of bacterial multidrug resistance, and represents a serious concern for human health. To obtain a better understanding of underlying regulatory mechanisms, we have dissected the transcriptional activation of the ATP-binding cassette (ABC) transporter BmrC/BmrD of the Gram-positive model bacterium Bacillus subtilis. By using promoter-GFP fusions and live cell array technology, we demonstrate a temporally controlled transcriptional activation of the bmrCD genes in response to antibiotics that target protein synthesis. Intriguingly, bmrCD expression only occurs during the late-exponential and stationary growth stages, irrespective of the timing of the antibiotic challenge. We show that this is due to tight transcriptional control by the transition state regulator AbrB. Moreover, our results show that the bmrCD genes are co-transcribed with bmrB (yheJ), a small open reading frame immediately upstream of bmrC that harbors three alternative stem-loop structures. These stem-loops are apparently crucial for antibiotic-induced bmrCD transcription. Importantly, the antibiotic-induced bmrCD expression requires translation of bmrB, which implies that BmrB serves as a regulatory leader peptide. Altogether, we demonstrate for the first time that a ribosome-mediated transcriptional attenuation mechanism can control the expression of a multidrug ABC transporter.
Type VI protein secretion system (T6SS) is important for bacterial competition through contact-dependent killing of competitors. T6SS delivers effectors to neighboring cells and corresponding antagonistic proteins confer immunity against effectors that are delivered by sister cells. Although T6SS has been found in more than 100 gram-negative bacteria including many important human pathogens, few T6SS-dependent effector and immunity proteins have been experimentally determined. Here we report a high-throughput approach using transposon mutagenesis and deep sequencing (Tn-seq) to identify T6SS immunity proteins in Vibrio cholerae. Saturating transposon mutagenesis was performed in wild type and a T6SS null mutant. Genes encoding immunity proteins were predicted to be essential in the wild type but dispensable in the T6SS mutant. By comparing the relative abundance of each transposon mutant in the mutant library using deep sequencing, we identified three immunity proteins that render protection against killing by T6SS predatory cells. We also identified their three cognate T6SS-secreted effectors and show these are important for not only antibacterial and antieukaryotic activities but also assembly of T6SS apparatus. The lipase and muramidase T6SS effectors identified in this study underscore the diversity of T6SS-secreted substrates and the distinctly different mechanisms that target these for secretion by the dynamic T6SS organelle.
The enzyme which confers resistance to erythromycin in the producing organism Streptomyces erythraeus dimethylates a single adenine residue in Bacillus stearothermophilus 23 S rRNA. This corresponds to residue Ade 2058 in Escherichia coli 23 S RNA. The methylase responsible for resistance to macrolides, lincomycin, and streptogramin B-related antibiotics in Staphylococcus aureus also acts at this site.
Although gram-positive infections account for the majority of cases of sepsis, the molecular mechanisms underlying their effects remains poorly understood. We investigated how cell wall components of gram-positive bacteria contribute to the development of sepsis. Experimental observations derived from cultured primary macrophages and the cell line indicate that gram-positive bacterial endotoxins induce hypoxia-inducible factor 1α (HIF-1α) mRNA and protein expression. Inoculation of live or heat-inactivated gram-positive bacteria with macrophages induced HIF-1 transcriptional activity in macrophages. Concordant with these results, myeloid deficiency of HIF-1α attenuated gram-positive bacterial endotoxin-induced cellular motility and proinflammatory gene expression in macrophages. Conversely, gram-positive bacteria and their endotoxins reduced expression of the myeloid anti-inflammatory transcription factor Krüppel-like transcription factor 2 (KLF2). Sustained expression of KLF2 reduced and deficiency of KLF2 enhanced gram-positive endotoxins induced HIF-1α mRNA and protein expression in macrophages. More importantly, KLF2 attenuated gram-positive endotoxins induced cellular motility and proinflammatory gene expression in myeloid cells. Consistent with these results, mice deficient in myeloid HIF-1α were protected from gram-positive endotoxin-induced sepsis mortality and clinical symptomatology. By contrast, myeloid KLF2-deficient mice were susceptible to gram-positive sepsis induced mortality and clinical symptoms. Collectively, these observations identify HIF-1α and KLF2 as critical regulators of gram-positive endotoxin-mediated sepsis.
A yeast strain lacking Met4p, the primary transcriptional regulator of the sulfur assimilation pathway, cannot synthesize methionine. This apparently simple auxotroph did not grow well in rich media containing excess methionine, forming small colonies on yeast extract/peptone/dextrose plates. Faster-growing large colonies were abundant when overnight cultures were plated, suggesting that spontaneous suppressors of the growth defect arise with high frequency. To identify the suppressor mutations, we used genome-wide single-nucleotide polymorphism and standard genetic analyses. The most common suppressors were loss-of-function mutations in OPI1, encoding a transcriptional repressor of phospholipid metabolism. Using a new system that allows rapid and specific degradation of Met4p, we could study the dynamic expression of all genes following loss of Met4p. Experiments using this system with and without Opi1p showed that Met4 activates and Opi1p represses genes that maintain levels of S-adenosylmethionine (SAM), the substrate for most methyltransferase reactions. Cells lacking Met4p grow normally when either SAM is added to the media or one of the SAM synthetase genes is overexpressed. SAM is used as a methyl donor in three Opi1p-regulated reactions to create the abundant membrane phospholipid, phosphatidylcholine. Our results show that rapidly growing cells require significant methylation, likely for the biosynthesis of phospholipids.
ScPif1 DNA helicase is the prototypical member of a 5'-to-3' helicase superfamily conserved from bacteria to human and plays various roles in the maintenance of genomic homeostasis. While many studies have been performed with eukaryotic Pif1 helicases, including yeast and human Pif1 proteins, the potential functions and biochemical properties of prokaryotic Pif1 helicases remain largely unknown. Here, we report the expression, purification and biochemical analysis of Pif1 helicase from Bacteroides sp. 3_1_23 (BsPif1). BsPif1 binds to a large panel of DNA substrates and, in particular, efficiently unwinds partial duplex DNAs with 5'-overhang, fork-like substrates, D-loop and flap-like substrates, suggesting that BsPif1 may act at stalled DNA replication forks and enhance Okazaki fragment maturation. Like its eukaryotic homologues, BsPif1 resolves R-loop structures and unwinds DNA-RNA hybrids. Furthermore, BsPif1 efficiently unfolds G-quadruplexes and disrupts nucleoprotein complexes. Altogether, these results highlight that prokaryotic Pif1 helicases may resolve common issues that arise during DNA transactions. Interestingly, we found that BsPif1 is different from yeast Pif1, but resembles more human Pif1 with regard to substrate specificity, helicase activity and mode of action. These findings are discussed in the context of the possible functions of prokaryotic Pif1 helicases in vivo.
In the yeast S. cerevisiae, ribosome assembly is linked to environmental conditions by the coordinate transcriptional regulation of genes required for ribosome biogenesis. In this study we show that two nonessential stress-responsive genes, YAR1 and LTV1, function in 40S subunit production. We provide genetic and biochemical evidence that Yar1, a small ankyrin-repeat protein, physically interacts with RpS3, a component of the 40S subunit, and with Ltv1, a protein recently identified as a substoichiometric component of a 43S preribosomal particle. We demonstrate that cells lacking YAR1 or LTV1 are hypersensitive to particular protein synthesis inhibitors and exhibit aberrant polysome profiles, with a reduced absolute number of 40S subunits and an excess of free 60S subunits. Surprisingly, both mutants are also hypersensitive to a variety of environmental stress conditions. Overexpression of RPS3 suppresses both the stress sensitivity and the ribosome biogenesis defect of Deltayar1 mutants, but does not suppress either defect in Deltaltv1 mutants. We propose that YAR1 and LTV1 play distinct, nonessential roles in 40S subunit production. The stress-sensitive phenotypes of strains lacking these genes reveal a hitherto unknown link between ribosome biogenesis factors and environmental stress sensitivity.
Bacterial lipopolysaccharide (LPS) triggers innate immune responses through Toll-like receptor (TLR) 4. We show here that the suppressor of cytokine-signaling-1 (SOCS1/JAB) is rapidly induced by LPS and negatively regulates LPS signaling. SOCS1(+/-) mice or SOCS1(-/-) mice with interferon-gamma (IFNgamma)-deficient background were more sensitive to LPS-induced lethal effects than were wild-type littermates. LPS-induced NO(2)(-) synthesis and TNFalpha production were augmented in SOCS1(-/-) macrophages. Furthermore, LPS tolerance, a protection mechanism against endotoxin shock, was also strikingly reduced in SOCS1(-/-) cells. LPS-induced I-kappaB and p38 phosphorylation was upregulated in SOCS1(-/-) macrophages, and forced expression of SOCS1 suppressed LPS-induced NF-kappaB activation. Thus, SOCS1 directly suppresses TLR4 signaling and modulates innate immunity.
OBJECTIVE The authors sought to determine innate immune system activation following psychosocial stress in patients with major depression and increased early life stress. METHOD Plasma interleukin (IL)-6, lymphocyte subsets, and DNA binding of nuclear factor (NF)-kB in peripheral blood mononuclear cells were compared in medically healthy male subjects with current major depression and increased early life stress (N=14) versus nondepressed male comparison subjects (N=14) before and after completion of the Trier Social Stress Test. RESULTS Trier Social Stress Test-induced increases in IL-6 and NF-kappaB DNA-binding were greater in major depression patients with increased early life stress and independently correlated with depression severity, but not early life stress. Natural killer (NK) cell percentages also increased following stress. However, there were no differences between groups and no correlation between NK cell percentage and stress-induced NF-kappaB DNA-binding or IL-6. CONCLUSIONS Male major depression patients with increased early life stress exhibit enhanced inflammatory responsiveness to psychosocial stress, providing preliminary indication of a link between major depression, early life stress and adverse health outcomes in diseases associated with inflammation.
A genetic interference phenomenon in the nematode Caenorhabditis elegans has been described in which expression of an individual gene can be specifically reduced by microinjecting a corresponding fragment of double-stranded (ds) RNA. One striking feature of this process is a spreading effect: interference in a broad region of the animal is observed following the injection of dsRNA into the extracellular body cavity. Here we show that C. elegans can respond in a gene-specific manner to dsRNA encountered in the environment. C. elegans normally feed on bacteria, ingesting and grinding them in the pharynx and subsequently absorbing bacterial contents in the gut. We find that Escherichia coli bacteria expressing dsRNAs can confer specific interference effects on the nematode larvae that feed on them.
Gram-negative bacteria have an outer membrane (OM) that functions as a barrier to protect the cell from toxic compounds such as antibiotics and detergents. The OM is a highly asymmetric bilayer composed of phospholipids, glycolipids, and proteins. Assembly of this essential organelle occurs outside the cytoplasm in an environment that lacks obvious energy sources such as ATP, and the mechanisms involved are poorly understood. We describe the identification of a multiprotein complex required for the assembly of proteins in the OM of Escherichia coli. We also demonstrate genetic interactions between genes encoding components of this protein assembly complex and imp, which encodes a protein involved in the assembly of lipopolysaccharides (LPS) in the OM. These genetic interactions suggest a role for YfgL, one of the lipoprotein components of the protein assembly complex, in a homeostatic control mechanism that coordinates the overall OM assembly process.
Abiotic and biotic stressors in human cells are often a result of sudden and/or frequent changes in environmental factors. The molecular response to stress involves elaborate modulation of gene expression and is of homeostatic, ecological, and evolutionary importance. Although attention has primarily focused on signaling pathways and protein networks, long non-coding RNAs (ncRNAs) are increasingly involved in the molecular mechanisms associated with responses to cellular stresses. We identified six novel short-lived long ncRNAs (MIR22HG, GABPB-AS1, LINC00152, IDI2-AS1, SNHG15, and FLJ33630) that responded to chemical stressors (cisplatin, cycloheximide, and mercury (II) oxide) in HeLa Tet-off cells. Our results indicate that short-lived long ncRNAs respond to general and specific chemical stressors. The expression levels of the short-lived long ncRNAs were elevated because of prolonged decay rates in response to chemical stressors and interruption of RNA degradation pathways. We propose that these long ncRNAs have the potential to be surrogate indicators of cellular stress responses.
Animal host defense against infection requires the expression of defense genes at the right place and the right time. Understanding such tight control of host defense requires the elucidation of the transcription factors involved. By using an unbiased approach in the model Caenorhabditis elegans, we discovered that HLH-30 (known as TFEB in mammals) is a key transcription factor for host defense. HLH-30 was activated shortly after Staphylococcus aureus infection, and drove the expression of close to 80% of the host response, including antimicrobial and autophagy genes that were essential for host tolerance of infection. TFEB was also rapidly activated in murine macrophages upon S. aureus infection and was required for proper transcriptional induction of several proinflammatory cytokines and chemokines. Thus, our data suggest that TFEB is a previously unappreciated, evolutionarily ancient transcription factor in the host response to infection.
Endogenous glucocorticoids (GC) play an important role in the termination of the inflammatory response following infection and tissue injury. However, recent findings indicate that stress can impair the anti-inflammatory capacities of these hormones. Lipopolysaccharide (LPS)-stimulated splenocytes of mice that were repeatedly subjected to social disruption (SDR) stress were less sensitive to the immunosuppressive effects of corticosterone (CORT) as demonstrated by an increased production of pro-inflammatory cytokines and enhanced cell survival. Myeloid cells expressing the marker CD11b were shown to play a key role in this process. Here we investigated the role of the bone marrow as a potential source of the GC-insensitive cells. The study revealed that LPS-stimulated bone marrow cells, in the absence of experimental stress, were virtually GC-resistant and retained high levels of cell viability after treatment with CORT. Recurrent exposure to the acute stressor over a period of 2, 4 or 6 days led to an increase in the GC sensitivity of the bone marrow cells. This increase in GC sensitivity was associated with enhanced mRNA expression of granulocyte-macrophage colony-stimulating factor (GM-CSF), an increase in the number of myeloid progenitors, and a decrease in the proportion of mature CD11b+ cells. The changes in the cellular composition of the bone marrow were accompanied by an increase in splenic CD11b+ cell numbers. Simultaneous assessment of the GC sensitivity in bone marrow and spleen revealed a significant negative correlation between both tissues suggesting that social stress causes the redistribution of GC-insensitive myeloid cells from the bone marrow to the spleen.
The coloured ciliate Blepharisma japonicum changes swimming velocity (positive photokinesis) and elongates its body in response to a prolonged illumination. We have recently proposed that alterations in the phosphorylation level of the ciliate phosducin (Pdc) may be involved in light-induced cell elongation, which in turn affects the interaction of βγ-dimer of G-proteins (Gβγ) with β-tubulin and subsequent cytoskeletal remodelling. The cellular mechanism that governs the photokinetic effect in this ciliate has not been elucidated. In the present study, we utilise real-time PCR to demonstrate that the levels of ciliate Pdc mRNA are significantly reduced in Pdc-RNAi-treated cells compared to cells fed with bacteria carrying the empty vector (control cells). Using western immunoblotting, we confirmed that these cells treated with Pdc-RNAi expressed a substantially lower level of the Pdc protein. The assay also revealed that in ciliates treated with Pdc-RNAi and exposed to light, the cytosolic level of Gβ (~36 kDa) was reduced, whereas the level of Gβ localized to the membrane (~32 kDa) was increased compared to control cells. In addition, behavioural analysis of the cells indicated a substantial reduction of photokinesis. The findings in this study provide additional characterization of the functional properties of the ciliate Pdc protein and we discuss a likely role for this phosphoprotein in the photokinetic phenomenon of the ciliate protist Blepharisma.