1,721,030 research outputs found
An integrated regulatory network including two positive feedback loops to modulate the activity of sigma(E) in mycobacteria
No full textsigma(E), one of the best characterized mycobacterial extracytoplasmic function sigma factors, is involved in virulence, surface stress response and modulation of the inflammatory response during infection. The regulation of its activity is very complex and involves transcriptional, translational and post-translational control. Post-translational regulation is controlled by RseA, an anti-sigma factor belonging to the zinc-associated anti-sigma factor family. In this issue of Molecular Microbiology, Barik et al. demonstrate that RseA is a redox-sensing protein that is able to bind sigma(E) only in reducing environment. Importantly, they describe a novel positive feedback loop responsible for sigma(E) release and activation following surface stress, due to ClpC1P2-dependent proteolytic degradation of RseA, depending on its phosphorylation by the eukaryotic-like Ser/Thr protein kinase PknB
ComEA is a DNA receptor for transformation of competent Bacillus subtilis.
No full textCompetent cells of Bacillus subtilis efficiently bind and internalize DNA. ComEA and the seven proteins encoded by the comG operon are required in vivo for the binding step. We show here that ComEA, a bitopic membrane protein, is itself capable of high-affinity DNA binding. A domain necessary for DNA binding is located at the C-terminus of ComEA. Proteins with similar 60-80 amino acid residue domains are widespread among bacteria and higher organisms. ComEA shows a marked preference for double-stranded DNA and can bind to oligomers as small as 22 bp in length. DNA binding by ComEA exhibits no apparent base sequence specificity. Using a membrane vesicle DNA-binding assay system we show that in the absence of cell wall, ComEA is still required for DNA binding, whereas the requirement for the ComG proteins is bypassed. We conclude that the ComG proteins are needed in vivo to provide access of the binding domain of ComEA to exogenous DNA. Possible specific roles for the ComG proteins are discussed
NucA is required for DNA cleavage during transformation of Bacillus subtilis
No full textWe have re-examined the roles of nucA and nin, in the transformation of Bacillus subtilis as conflicting accounts have been presented concerning the importance of these genes for transformation. The present report demonstrates that nucA deficiency lowers the rate of DNA transport and that NucA is needed for the double-strand cleavage of transforming DNA, probably acting directly as an endonuclease. A relative paucity of DNA termini, resulting from the absence of this endonuclease activity, most probably accounts for the decreased transport rate. NucA is a bitopic integral membrane protein, with its C-terminus external to the membrane where it is appropriately located to effect the cleavage of bound transforming DNA. We have also investigated the roles of the known competence genes in the DNA processing that accompanies transformation in B. subtilis. The genes that are required for DNA transport (comEA, comEC and comFA) are also required for the degradation of the non-transforming strand that accompanies internalization, but comEC and comFA are not needed for the double-strand cleavage that occurs external to the cell membrane
A macromolecular complex formed by a pilin-like protein in competent Bacillus subtilis.
Full text linkIn competent Bacillus subtilis, the ComG proteins are required to allow exogenous DNA to access to membrane-bound receptor ComEA during transformation. Here we describe a multimeric complex containing the pilin-like protein ComGC. Due to similarities to the type 4 pilus and the type 2 secretion system pseudopilus, we have tentatively named it the "competence pseudopilus." The ComGC multimer is released from cells upon digestion of the cell wall with lysozyme and has a heterogeneous size, estimated to range between 40 and 100 monomers, covalently linked by disulfide bonds. We determined that the prepilin peptidase ComC, the thiol-disulfide oxidoreductase pair BdbDC, and all seven ComG proteins are necessary to form the pseudopilus. Furthermore, these proteins are also sufficient to form a functional complex, i.e. able to facilitate binding of exogenous DNA to ComEA. The initial steps of pseudopilus biogenesis include the processing of ComGC in the cytoplasmic membrane and consist of two independent events, proteolytic cleavage by ComC and formation of an intramolecular disulfide bond by BdbDC. The other ComG proteins are required to assemble the mature ComGC monomers in the membrane into a multimeric complex proposed to span the cell envelope. We discuss the possible role of the competence pseudopilus in DNA binding and uptake during transformation
Internalizing DNA
No full textThe steps involved in the transformation of Bacillus subtilis are reviewed. These include the initial binding, processing and passage of DNA across the cell wall and transport across the plasma membrane. Our understanding of the roles of the proteins known to be required for these steps is reviewed
Mycobacterium tuberculosis requires the ECF sigma factor SigE to arrest phagosome maturation.
Full text linkThe sigma factors of Mycobacterium tuberculosis
No full textMycobacterium tuberculosis is a remarkable pathogen capable of adapting and surviving in various harsh conditions. Correct gene expression regulation is essential for the success of this process. The reversible association of different sigma factors is a common mechanism for reprogramming bacterial RNA polymerase and modulating the transcription of numerous genes. Thirteen putative sigma factors are encoded in the M. tuberculosis genome, several being important for virulence. Here, we analyse the latest information available on mycobacterial sigma factors and discuss their roles in the physiology and virulence of M. tuberculosis
Characterization of conjugative transposon Tn5251 of Streptococcus pneumoniae
No full textTn5251 belongs to the Tn916-Tn1545 family of conjugative transposons (CT) and was found integrated into CT Tn5252, to form the composite element Tn5253 of Streptococcus pneumoniae. We show that Tn5251 is identical in structure and size to Tn916. DNA sequence analysis of a 4,419-bp segment containing the tet(M) gene showed that only 73 nucleotides out of 4,419 were different in the two CT. Essentially all differences (66/73) were clustered in a 688-bp segment of tet(M), which was 90% identical to Tn916 and 100% identical to the tet(M) genes of Tn1545 from S. pneumoniae and pOZ101 from Neisseria gonorrhoeae. DNA sequence analysis of the Tn5251/Tn5252 junction fragments allowed us (i) to determine Tn5251 termini, (ii) to define the 6-bp coupling sequences flanking the CT, and (iii) to infer the structure of the integration site (attB) of Tn5251 into Tn5252. Conjugal transfer of Tn5251 independent from Tn5253 could not be detected, even if we could show excision and formation of Tn5251 circular intermediates at a level of 5.4 copies per 10(6) chromosomes
Rv2358 and FurB: Two transcriptional regulators from Mycobacterium tuberculosis which respond to zincl
No full textIn a previous work, we demonstrated that the Mycobacterium tuberculosis Rv2358-furB operon is induced by zinc. In this study, the orthologous genes from Mycobacterium smegmatis mc(2)155 were inactivated and mutants analyzed. Rv2358 protein was purified and found to bind upstream of the Rv2358 gene. Binding was inhibited by Zn(2+) ions
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