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Divergent orientation of transcription from the biotin locus of Escherichia coli

1971; Elsevier BV; Volume: 56; Issue: 1 Linguagem: Inglês

10.1016/0022-2836(71)90083-0

1089-8638

Arabinda Guha, Y. Saturen, Waclaw Szybalski,

Biotin and Related Studies

Pulse-labeled [3H]RNA produced by the bio locus of Escherichia coli grown in biotin-free medium hybridizes with both DNA strands of λbiot124, a bio-transducing phage that contains the entire bio locus, with an l:r strand ratio of 25:75 (fully derepressed in bio− mutants) or 40:60 (partially repressed by endogenous biotin in bio+ cells). When employing DNA strands of λbio1, which contains only genes A and B, the latter l:r ratio becomes 89:11, with the amount of [3H]RNA hybridizing with the l strand remaining unchanged. These results indicate that both strands of the bio locus are transcribed and the orientation of the two transcriptions is divergent, with cistron A belonging to the leftward (counter-clockwise) transcribed operon, and the other bio cistrons forming a rightward (clockwise) oriented operon. The bio transcription from both strands is subject to co-ordinate repression by biotin. The bio[3H]RNA amounts to as much as 0.6% of the total pulse-labeled RNA in fully derepressed E. coli bio− cells, and is reduced to approximately 0.2% in bio+ cells grown in biotin-free medium, and to undetectable amounts in medium supplemented with more than 2 × 10−3 μg biotin/ml. Desthiobiotin does not act as a corepressor unless converted to biotin.