ComK protein of
Bacillus subtilis positively regulates the transcription of several late competence genes as well as
comK itself. We constructed a
clpX disrupted mutant of
B. subtilis and studied its effect on the regulation of ComK activation. When P
spac, which controls the
comK gene in a multicopy plasmid, was induced by the addition of IPTG,
comK transcripts were detected in both the
clpX mutant and the wild type. However, the ComK protein could not be detected in the
clpX disrupted mutant. To obtain further information, we constructed several
comK-lacZ translational fusions covering different lengths of the
comK gene, whose transcription is controlled by an IPTG inducible P
spac promoter. We found that both the expression of
comK-lacZ directed β-galactosidase and the accumulation of ComK-LacZ fused protein, derived from the fusion containing the entire
comK open reading frame, were extremely reduced in the
clpX mutant compared with the wild type, while the accumulation of
comK-lacZ transcripts in the
clpX mutant after the addition of IPTG was about half that in the
clpX+background. On the other hand, transcription, translation and activity of
comK-lacZ were detected in both the
clpX mutant and the wild type when the
comK-lacZ fusion lacking the 3' region of the
comK gene was induced. These results indicate that ClpX plays an important role in the regulation of ComK at the post-transcriptional level.
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