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Cell. 1993 Jun 18;73(6):1165-73.

LexA and lambda Cl repressors as enzymes: specific cleavage in an intermolecular reaction.

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Department of Biochemistry, University of Arizona, Tucson 85721.


During the SOS response, LexA repressor is inactivated by specific cleavage. Although cleavage requires RecA protein in vivo, RecA acts indirectly as a coprotease by stimulating an inherent self-cleavage activity of LexA. In lambda lysogens, cleavage of lambda Cl repressor in a similar but far slower reaction results in prophage induction. We describe an intermolecular cleavage reaction in which the C-terminal fragment of LexA acted as an enzyme to cleave other molecules of LexA. The C-terminal fragment of lambda repressor cleaved the LexA substrates about as efficiently as did the LexA enzyme, suggesting that the slow rate of Cl self-cleavage results from a weak interaction between its cleavage site and the active site.

[Indexed for MEDLINE]

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