SPO0A REPRESSES TRANSCRIPTION OF THE CRY TOXIN GENES IN BACILLUS-THURINGIENSIS

The DNA regions upstream from the genes encoding polypeptides of Bacil lus thuringiensis subsp. israelensis larvicidal crystals (cry4A, cry4B , cry11A) contain sequences with similarities to the spo0A box of Baci llus subtilis (or '0A' box) and the promoter recognized by the sigma(H )-associated RNA polymerase of B. subtilis. Expression of cry-lacZ tra nscriptional fusions was analysed in various B. thuringiensis genetic backgrounds. The early transcription of the toxin genes was not sporul ation-dependent, whereas the late-stage expression at t(4-6) was sigma (E)-dependent. Primer extension analysis confirmed that the cry4- and cry11-type toxin genes were weakly transcribed during the transition p hase; expression analysis of a cry11A'-lacZ transcriptional fusion in B. subtilis sporulation mutants confirmed the involvement of the sigma (H)-RNA polymerase. Primer extension analysis showed that in B. thurin giensis subsp. israelensis. the cry4A and cry11A gene transcription ob served at the end of the growth stage was turned off at the beginning of the sporulation phase. The DNA region located upstream from the cry 11A gene promoter including the putative '0A' box was deleted. This le d to a derepression of the expression of the cry11A operon. These resu lts suggest that the cry4A, cry4B and cry11A toxin genes of B. thuring iensis subsp. israelensis are transcribed during the transition phase by the RNA polymerase associated with the sigma(H) factor and are subj ect to Spo0A repression.