GENETIC-ANALYSIS OF CRYIIIA GENE-EXPRESSION IN BACILLUS-THURINGIENSIS

The Bacillus thuringiensis (Bt) crylllA gene is regulated by a differe nt mechanism from that of most of the other cry genes. Its expression begins during late-exponential growth and not during sporulation as fo r the other classes of cry genes. Moreover, in Bacillus subtilis, cryl llA expression is independent of the major sporulation-specific sigma factors and is increased in a spoOA genetic background, We used lacZ f usions and primer-extension analysis to follow the time-course of cryl llA transcription in Bt wild-type and in various Spo(-) genetic backgr ounds (spoOA, sigE and sigK). crylllA was activated from the end of ve getative growth to stage II of sporulation (t(3)) in the wild-type str ain. Thereafter, transcription from the same promoter continued, at a decreasing rate, until the end of stage III. In the spoOA mutant strai n, the same promoter was activated for at least 15 h during the statio nary phase, crylllA activation in the sigK genetic background was simi lar to that in the wild-type but was extended in a sigE mutant strain. Thus crylllA expression in Bt is not directly dependent on the major sporulation-specific sigma factors. Furthermore, an event linked with the sigma(E)-dependent period of sporulation ends crylllA activation, although transcription of this gene does not switch off before the end of stage III.