This chapter examines cleavage of LexA repressor. In normally growing cells, about 20 SOS genes are turned off by the LexA repressor. On inducing treatments, LexA undergoes specific proteolytic cleavage; cleavage inactivates LexA and leads to derepression of the SOS genes. This specific cleavage reaction is of biological interest as it controls the state of the SOS regulatory system. Lex A cleavage is catalyzed in vivo and at neutral pH in vitro, by interaction with another regulatory protein, RecA, which is activated in vivo by inducing treatments. The use of mutant proteins with an increased rate of cleavage allows the development of an intermolecular cleavage reaction in which one molecule of LexA acts as an enzyme to attack other molecules. LexA is 22.7 kDa in size and is organized into two structural and functional domains separated by a hinge region. LexA N-terminal region is the DNA binding domain; its C-terminal domain contains the contacts for dimerization, and all the elements necessary for specific cleavage. The cleavage site, Ala84-Gly85, lies in the hinge region. A tryptic fragment comprising residues 68-202 undergoes both autodigestion and RecA-mediated cleavage at normal rates.
ASJC Scopus subject areas
- Molecular Biology