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Cleavage of the lambda and P22 repressors by recA protein.

1982; Elsevier BV; Volume: 257; Issue: 8 Linguagem: Inglês

10.1016/s0021-9258(18)34744-6

1083-351X

Robert T. Sauer, Michael J. Ross, Mark Ptashne,

Genomics and Chromatin Dynamics

The site of recA cleavage of the phage X and P22 repressors has been determined.Each repressor is cut once by the recA enzyme, X repressor between residues 111 and 112, and P22 repressor between residues 94 and 95.recA cleavage occurs at identical alanyl-glycyl sequences in both repressors, and in both repressors, the cleavage separates the repressor's NHz-terminal DNA-binding domain from its COOH-terminal oligomerization domain.A papain-generated proteolytic fragment of X repressor consisting of repressor residues 93-236 is also efficiently cleaved by recA protein.Moreover, the recA cleavage of radioactive X repressor can be inhibited by certain COOH-terminal proteolytic fragments of X repressor which do not contain the alanyl-glycyl cleavage sequence.These facts suggest that recA cleavage of X repressor requires an intact COOH-terminal domain but not an intact NHz-terminal domain.Temperate phages, such as h and P22, form lysogens in which the phage DNA is integrated into the bacterial host chromosome, and transcription of most phage genes is repressed (1,2).When such lysogens are treated with UV light or certain activated carcinogens, the phage-encoded repressor is cleaved and the prophase induced (3).Neither cleavage of the repressor protein nor induction of the prophage occurs if the host cell bears certain recA-mutations or if the phage repressor bears an indmutation.Roberts and his colleagues have shown that purified recA protein cleaves h or P22 repressor in a reaction dependent upon single-stranded polynucleotide and nucleotides such as ATP or adenosine 5'-0-(3thiotriphosphate) (4-8).The h and P22 repressors share amino acid sequence homology (9, lo), and each contains two structural domains (ll).' The NHz-terminal domains function in binding operator DNA (12), while the COOH-terminal domains mediate repressor dimerization (11).The functions of both domains are essential for strong binding to operator DNA.Monomeric NHz-terminal fragments of A repressor bind operator DNA only weakly, and analysis of the concentration dependence of repressor binding to operator suggests that dimers of repressor