Attenuation of transcription of biotin genes in Escherichia coli.

The nature of RNA synthesis from the divergent bioA:BFCD operon has been studied in vivo in Escherichia coli minicells. Minicells containing bio-recombinant plasmids produce 96 nucleotide long RNA. This small RNA was characterized by blotting on diazobenzyloxymethyl cellulose paper and hybridization with the appropriate bio-probe DNA. Determination of beta-galactosidase, using biotin requiring mutant cells of E. coli JM101 infected with a bio-M13 recombinant phage containing the functional bioB region of the operon, demonstrated the presence of a transcription termination site in the bioBFCD segment. There was a three- to five-fold reduction in beta-galactosidase activity in this system at an appropriate d-biotin concentration which indicated that the early termination of transcription is biotin dependent. From the nucleotide sequence of the promoter proximal region of the bioB gene, a 13-oligonucleotide sequence believed to be the early transcription termination site has been located. A model of regulation at termination has been proposed on the basis of the not-too-stable RNA secondary structure at the site of early termination of transcription.