ISSN:
1365-2958
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Medicine
Notes:
The important human pathogen Streptococcus pyogenes (the group A streptococcus or GAS) causes diseases ranging from mild, self-limiting pharyngitis to severe invasive infections. Regulation of the expression of GAS genes in response to specific environmental differences within the host is probably key in determining the course of the infectious process, however, little is known of global regulators of gene expression in GAS. Although secondary RNA polymerase sigma factors act as global regulators of gene expression in many other bacteria, none has yet been isolated from the GAS. The newly available GAS genome sequence indicates that the only candidate secondary sigma factor is encoded by two identical open reading frames (ORFS). These ORFS encode a protein that is 40% identical to the transcription factor ComX, believed to act as an RNA polymerase sigma factor in Streptococcus pneumoniae. To test whether the GAS ComX homologue functions as a sigma factor, we cloned and purified it from Escherichia coli. We found that in vitro, this GAS protein, which we call σX, directed core RNA polymerase from Bacillus subtilis to transcribe from two GAS promoters that contain the cin-box region, required for transcription by S. pneumoniae ComX in vivo. On the other hand, GAS σX did not promote transcription of a GAS promoter (hasA) expected to be dependent on σA, the housekeeping or primary RNA polymerase sigma factor. Addition of monoclonal antibody that inhibited σA-directed transcription had no effect on σX-directed transcription, showing that the latter was not the result of contaminating σA. Transcription of both cin-box-containing promoters initiated downstream of the cin-box and two different single basepair substitutions in the cin-box of the cinA promoter each caused a severe reduction of σX-directed transcription in vitro. Thus, the cin-box is required for σX-directed transcription.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1365-2958.2001.02657.x
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