A Role for the RNA Polymerase Gene Specificity Factor s 54 in the Uniform Colony Growth of Uropathogenic Escherichia coli

Abstract

The canonical function of a bacterial sigma (s ) factor is to determine the gene specificity of the RNA polymerase (RNAP). In several diverse bacterial species, the s 54 factor uniquely confers distinct functional and regulatory properties on the RNAP. A hallmark feature of the s 54-RNAP is the obligatory requirement for an activator ATPase to allow transcription initiation. Different activator ATPases couple diverse environmental cues to the s 54-RNAP to mediate adaptive changes in gene expression. Hence, the genes that rely upon s 54 for their transcription have a wide range of different functions suggesting that the repertoire of functions performed by genes, directly or indirectly affected by s 54, is not yet exhaustive. By comparing the growth patterns of prototypical enteropathogenic, uropathogenic, and nonpathogenic Escherichia coli strains devoid of s 54, we uncovered that the absence of s 54 results in two differently sized colonies that appear at different times specifically in the uropathogenic E. coli (UPEC) strain. Notably, UPEC bacteria devoid of individual activator ATPases of the s 54-RNAP do not phenocopy the s 54 mutant strain. Thus, it seems that s 54's role as a determinant of uniform colony appearance in UPEC bacteria represents a putative non-canonical function of s 54 in regulating genetic information flow.