Genetic analysis of the promoter region of the Bacillus subtilis alpha-amylase gene.

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RESUMO

The amyR2 allele of the Bacillus subtilis alpha-amylase cis-regulatory region enhances production of amylase and transcription of amyE, the structural gene, by two- to threefold over amyR1. The amylase gene bearing each of these alleles was cloned on plasmids of about 10 to 15 copies per chromosome. Transcription of the cloned amylase gene by each amyR allele was activated at the end of exponential growth and was subject to catabolite repression by glucose. The amount of amylase produced was roughly proportional to the copy number of the plasmid, and cells containing the amyR2-bearing plasmid, pAR2, produced two- to threefold more amylase than cells with the amyR1 plasmid, pAMY10. Deletion of DNA 5' to the alpha-amylase promoter, including deletion of the A + T-rich inverted repeat found in amyR1 and amyR2, had no effect on expression or transcription of alpha-amylase. Deletion of DNA 3' to the amyR1 promoter did not impair temporal activation of chloramphenicol acetyltransferase in amyR1-cat-86 transcriptional fusions, but catabolite repression was abolished. When an 8-base-pair linker was inserted in pAMY10 at the same site from which the 3' deletion was made, amylase expression doubled and was repressed less by glucose. Both the deletion and the insertion disrupted four bases at the 3' end of the putative amylase operator region. Site-directed mutagenesis was used to change bases in the promoter-operator region of amyR1 to their amyR2 counterparts. Either change alone increased amylase production twofold, but only the change at +7, next to the linker insertion of 3' deletion site, yielded the increased amylase activity in the presence of glucose that is characteristic of the amyR2 strain. The double mutant behaved most like strains carrying the amyR2 allele.

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