Identification and characterization of the gene encoding the Acidobacterium capsulatum major sigma factor

Acidobacterium capsulatum is an acid-tolerant, encapsulated, Gram-negative member of the ubiquitous, but poorly understood Acidobacteria phylum. Little is known about the genetics and regulatory mechanisms of A. capsulatum. To begin to address this gap, we identified the gene encoding the A. capsulatum major sigma factor, rpoD, which encodes a 597-amino acid protein with a predicted sequence highly similar to the major sigma factors of Solibacter usitatus Ellin6076 and Geobacter sulfurreducens PCA. Purified hexahistidine-tagged RpoD migrates at approximately 70 kDa under SDS-PAGE conditions, which is consistent with the predicted MW of 69.2 kDa, and the gene product is immunoreactive with monoclonal antibodies specific for either bacterial RpoD proteins or the N-terminal histidine tag. A. capsulatum RpoD restored normal growth to E. coli strain CAG20153 under conditions that prevent expression of the endogenous rpoD. These results indicate we have cloned the gene encoding the A. capsulatum major sigma factor and the gene product is active in E. coli.     

Multiple rpoD-related genes of cyanobacteria.

Genomes of many eubacterial strains have been shown to encode for multiple rpoD-related genes. In this report, we describe the identification of the multiple rpoD-related genes of cyanobacterial strains. DNAs of three cyanobacterial strains, Anabaena sp. PCC7120, Synechococcus sp. PCC7942, and Synechocystis sp. PCC6803, were examined by Southern hybridization, using a synthetic probe designed for detecting rpoD or rpoD-related genes. Four or five hybridization signals were found in each DNA. Four DNA regions of Synechococcus sp. PCC7942 corresponding to the hybridization signals were cloned and partially sequenced. The sequence data indicate the presence of genes, named rpoD1, rpoD2, rpoD3, and rpoD4, whose products are highly similar to the basic structure of the principal sigma factors of eubacterial strains. The rpoD1 gene showed the greatest similarity to the sigA gene of Anabaena sp. PCC7120.     

Amplification of the housekeeping sigma factor in Pseudomonas fluorescens CHA0 enhances antibiotic production and improves biocontrol abilities.

Pseudomonas fluorescens CHA0 produces a variety of secondary metabolites, in particular the antibiotics pyoluteorin and 2,4-diacetylphloroglucinol, and protects various plants from diseases caused by soilborne pathogenic fungi. The rpoD gene encoding the housekeeping sigma factor sigma 70 of P. fluorescens was sequenced. The deduced RpoD protein showed 83% identity with RpoD of Pseudomonas aeruginosa and 67% identity with RpoD of Escherichia coli. Attempts to inactivate the single chromosomal rpoD gene of strain CHA0 were unsuccessful, indicating an essential role of this gene. When rpoD was carried by an IncP vector in strain CHA0, the production of both antibiotics was increased severalfold and, in parallel, protection of cucumber against disease caused by Pythium ultimum was improved, in comparison with strain CHA0.     

The response regulator RpaB binds the high light regulatory 1 sequence upstream of the high-light-inducible <Emphasis Type="Italic">hliB</Emphasis> gene from the cyanobacterium <Emphasis Type="Italic">Synechocystis</Emphasis> PCC 6803

Cyanobacteria, like other photosynthetic organisms, respond to the potentially damaging effects of high-intensity light by regulating the expression of a variety of stress-responsive genes through regulatory mechanisms that remain poorly understood. The high light regulatory 1 (HLR1) sequence can be found upstream of many genes regulated by high-light (HL) stress in cyanobacteria. In this study, we identify the factor that binds the HLR1 upstream of the HL-inducible hliB gene in the cyanobacterium Synechocystis PCC 6803 as the RpaB (Slr0947) response regulator.     

Environmental control of phosphorylation pathways in a branched two-component system

NblS, the most conserved histidine kinase in cyanobacteria, regulates photosynthesis and acclimatization to a variety of environmental conditions. We used in silico, in vivo and in vitro approaches to identify RpaB and SrrA as the cognate response regulators of NblS and to characterize relevant interactions between components of this signalling system. While genetic analysis showed the importance of the NblS to RpaB phosphorylation branch for culture viability in Synechococcus elongatus PCC 7942, in vitro assays indicated a strong preference for NblS to phosphorylate SrrA. This apparent discrepancy can be explained by environmental insulation of the RpaB pathway, achieved by RpaB-dependent repression of srrA under standard, low light culture conditions. After a strong but transient increase in srrA expression upon high light exposure, negative regulation of srrA and other high light inducible genes takes place, suggesting cooperation between pathways under environmental conditions in which both RpaB and SrrA are present. Complex regulatory interactions between RpaB and SrrA, two response regulators with a common evolutionary origin that are controlled by a single histidine kinase, are thus emerging. Our results provide a paradigm for regulatory interactions between response regulators in a branched two-component system.     

Principal sigma subunit of the Caulobacter crescentus RNA polymerase.

We have identified the gene encoding the Caulobacter crescentus principal sigma subunit, RpoD. The rpoD gene codes for a polypeptide of 653 amino acids with a predicted molecular mass of 72,623 Da (sigma 73). The C. crescentus sigma subunit has extensive amino acid sequence homology with the principal sigma factors of a number of divergent procaryotes. In particular, the segments designated region 2 that are involved in core polymerase binding and promoter recognition were identical among these bacteria despite the fact that the -10 region recognized by the C. crescentus sigma 73 differs significantly from that of the other bacteria. Thus, it appears that additional sigma factor regions must be involved in -10 region recognition. This conclusion was strengthened by a heterologous complementation assay in which C. crescentus sigma 73 was capable of complementing the Escherichia coli rpoD285 temperature-sensitive mutant. Furthermore, C. crescentus sigma 73 conferred new specificity on the E. coli RNA polymerase, allowing the expression of C. crescentus promoters in E. coli. Thus, the C. crescentus sigma 73 appears to have a broader specificity than does the sigma 70 of the enteric bacteria.