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Control of transcription by the bacteriophage P22 repressor

1982; Elsevier BV; Volume: 157; Issue: 1 Linguagem: Inglês

10.1016/0022-2836(82)90511-3

1089-8638

Anthony R. Poteete, Mark Ptashne,

Protein Structure and Dynamics

Bacteriophage P22 repressor regulates transcription from two divergent promoters, PRand PRM, by binding to three sites in the right operator of the phage. Repressor binding depends on the intrinsic affinities of the sites and on pairwise co-operative interactions between adjacently bound repressors. In the case of wild-type OR, repressor binds with the affinity order: OR1 − OR2 > OR3. With repressor bound to OR1 and OR2, the early lytic promoter, PR, is turned off and the lysogenic maintenance promoter, PRM, is turned on. This positive control of PRM results, at least in part, from direct stimulation of transcription by repressor bound to OR2. At high concentrations, repressor binds to OR3 and turns off PRM. The level of repressor in a lysogen is such that OR1 and OR2 are almost completely occupied, and OR3 is about 50% occupied. The mechanisms of action of P22 and λ phage repressors at their respective OR regions are quite similar, although the OR regions differ significantly in structure. A comparison of the phosphate contacts made by both repressors at their OR2 sites suggests that for both phages, positive control of PRM results from contact of the same part of RNA polymerase by different parts (with respect to the DNA-binding parts) of the two repressors.