A mutant LexA repressor harboring a cleavage motif cysteine-glycine remains inducible.

Using site-directed mutagenesis of the lexA gene we have changed the amino acid Ala-84 of the LexA repressor for a cysteine. The reason for this change was the striking homology between LexA and UmuD and the comparable size of the two amino acid side chains. Using an in vivo repression/induction assay it is shown that the LexA-Cys-84 mutant remains inducible by mitomycin C and UV irradiation essentially in the same way as the wild-type repressor.