COMK ACTS AS AN AUTOREGULATORY CONTROL SWITCH IN THE SIGNAL-TRANSDUCTION ROUTE TO COMPETENCE IN BACILLUS-SUBTILIS

The comK gene is a regulatory transcription unit which is essential fo r the development of genetic competence in Bacillus subtilis. The tran scription of comK is under strict nutritional and growth phase-depende nt control and has been shown to depend on the gene products of comA a nd srfA. In this report, we show that expression of comK is dependent on its own gene product as well as on the gene products of all other t ested regulatory genes known to be involved in competence development (abrB, comA, comP, degU, sin, spoOA, spoOH, spoOK, and srfA). A mecA m utation is able to suppress the competence deficiency of mutations in any of these regulatory loci except for mutations in spoOA and, as we show here, in comK. Furthermore, we show that the presence of comK on a multiple copy plasmid leads to derepression of comK expression, caus ing an almost constitutive expression of competence in minimal medium as well as permitting competence development in complex medium. We inf er from these results that the signals which trigger competence develo pment, after having been received and processed by the various compone nts of the competence signal transduction pathway, all converge at the level of comK expression. As soon as derepression of comK expression occurs, the positive autoregulation rapidly results in accumulation of the comK gene product, which subsequently induces competence.