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Repressor structure and the mechanism of positive control

1983; Cell Press; Volume: 32; Issue: 2 Linguagem: Inglês

10.1016/0092-8674(83)90451-8

1097-4172

Ann Hochschild, Nina Irwin, Mark Ptashne,

Bacterial Genetics and Biotechnology

It has been suggested that the λ repressor stimulates transcription of its own gene by binding to the λ operator and contacting RNA polymerase bound to the adjacent promoter. We describe three different mutants (called pc) of the λ phage repressor that are specifically deficient in the positive control function. We show that the amino acid residues altered in the pc mutants lie on the surface of the DNA-bound repressor that we predict, based on structural and other evidence, would most closely approach DNA-bound polymerase. Furthermore, we describe a pc mutant of the P22 repressor. We argue that in both the λ and P22 repressors a structure comprised of two alpha helices has two functions: to bind DNA and to contact RNA polymerase. In the two cases, however, different regions of this structure contact polymerase to mediate positive control.