Organization and transcription of the principal sigma gene (rpoDA) of Pseudomonas aeruginosa PAO1: involvement of a sigma 32-like RNA polymerase in rpoDA gene expression

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Abstract
S1 nuclease mapping and Northern (RNA) hybridization revealed that the rpoDA gene encoding the principal sigma subunit of Pseudomonas aeruginosa PAO1 is transcribed as a monocistronic mRNA of 2 kb and that the transcription from the rpoDA promoter (PC) starts 32 bases upstream from the first nucleotide of the initiation codon during the steady-state growth condition at a low temperature (30 degrees C). The transcript terminates 31 bases downstream from the last nucleotide of the termination codon. When the growth temperature was shifted to 42 degrees C, the synthesis of rpoDA mRNA from a heat shock promoter was transiently induced, although transcription was still occurring from PC during the heat shock period. The transcription initiation site of the heat shock promoter (PHS) is located about 220 bases upstream of the initiation codon of rpoDA. In addition, both promoters were utilized in vitro by RNA polymerase partially purified from heat-shocked cells of P. aeruginosa PAO1. When the rpoDA was introduced into Escherichia coli, the transcription patterns of rpoDA at 30 and 42 degrees C were similar to those observed for P. aeruginosa. These results suggested that the transcription of rpoDA in P. aeruginosa is regulated by the principal RNA polymerase and the heat shock RNA polymerase in response to the environmental temperature.