A genetic screen for isolating "lariat" Peptide inhibitors of protein function.

Functional genomic analyses provide information that allows hypotheses to be formulated on protein function. These hypotheses, however, need to be validated using reverse genetic approaches, which are difficult to perform on a large scale and in diploid organisms. We developed a genetic screen for isolating "lariat" peptides that function as trans dominant inhibitors of protein function. A lariat consists of a lactone-cyclized peptide with a covalently attached transcription activation domain, which allows combinatorial lariat libraries to be screened for protein interactions using the yeast two-hybrid assay. We isolated lariats against the bacterial repressor protein LexA. LexA regulates bacterial SOS response and LexA mutants that cannot undergo autoproteolysis make bacteria more sensitive to, and inhibit resistance against, cytotoxic reagents. We showed that an anti-LexA lariat blocked LexA autoproteolysis and potentiated the antimicrobial activity of mitomycin C.