TheBacillus subtilisLate Competence OperoncomEIs Transcriptionally Regulated byyutBand under Post-Transcription Initiation Control bycomN(yrzD)

Abstract

The Bacillus subtilis genome has been sequenced, and disruptants with disruptions in genes that were not characterized previously were systematically generated. We screened these gene disruptants for decreased transformation frequency and identified two genes, yrzD and yutB, whose disruption resulted in severely reduced transformation frequency and modestly reduced transformation frequency, respectively. In the regulation of competence development, various signals affect the expression of comK, which encodes a master regulator of genetic competence that drives late competence gene transcription. Epistatic analyses of both the yrzD and yutB genes revealed no significant differences in the expression of comK. Further analysis of the expression of late competence genes in the yrzD disruptant revealed that yrzD is specifically required for regulation of the comE operon, which is one of the late competence operons, and thus was renamed comN. An analysis of various comE-lacZ fusions revealed that the target cis element for comN action is in the large (approximately 1-kb) 5' untranslated region of comE, while the activity of the comE promoter was not affected by disruption of comN. These results suggested that there is post-transcription initiation control of comE by comN. A sequential deletion analysis of this region revealed the 35-bp region required for comN action. The yutB gene encodes a putative lipoic acid synthetase and yet is specifically required for transcription of comE, based on the results of lacZ fusion analyses. Therefore, yutB and comN regulate comE at the transcription and post-transcription initiation levels, respectively. These results demonstrate that a comE-specific regulatory mechanism is involved in development of genetic competence.