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J. Bacteriol., Dec 1995, 6854-6860, Vol 177, No. 23
J Malakooti and B Ely
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.
Copyright © 1995, American Society for Microbiology
Principal sigma subunit of the Caulobacter crescentus RNA polymerase
Department of Biological Sciences, University of South Carolina, Columbia 29208, USA.
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