1887

Abstract

The Fe(III)-reducing micro-organism requires an outer-membrane -type cytochrome, OmcB, for Fe(III) reduction, but a related cytochrome, OmcC, which is 73 % identical to OmcB, is not required. The and genes are part of a tandem chromosomal duplication consisting of two repeated clusters of four genes. The 2·7 kb sequences preceding and are identical with the exception of a single base pair change. Studies that combined genetic, Northern blotting and primer extension analyses demonstrated that both and are transcribed as monocistronic and polycistronic (--/) transcripts. All of the promoters for the various transcripts were found to be located within the 2·7 kb identical region upstream of and . The sequences of the promoter regions for the two monocistronic transcripts are identical and equidistant from the or start codons. The promoters for the two polycistronic transcripts, in contrast, are distinct. One is specific for transcription of -- and the other is associated with transcription of --. Studies with an RpoS-deficient mutant suggested that transcription from all four promoters is RpoS dependent under one or more growth conditions. Deletion of , a gene immediately upstream of -- that encodes a putative transcriptional regulator, significantly lowered the transcription when Fe(III) was the electron acceptor and partially inhibited Fe(III) reduction. In contrast, levels of transcripts were unaffected in the mutant. These results indicate that and operons represent a rare instance in which duplicated operons, located in tandem on the chromosome, have different transcriptional regulation.

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2005-06-01
2019-08-21
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