Dissection of bacteriophage lambda site-specific recombination using synthetic peptide combinatorial libraries.

A wide variety of tools have been used to dissect biochemical pathways, inhibitors being chief among them. Combinatorial approaches have made the search for inhibitors much more efficient. We have applied such an approach to identify hexapeptides which inhibit different steps in a site-specific recombination reaction mediated by the bacteriophage lambda integrase protein. Integrase's mechanism is still incompletely understood, in large part because several pathway intermediates remain hard to isolate. Integrase-catalyzed recombination is very efficient, but if blocked, it is highly reversible to substrates; this combination makes some intermediates exceedingly transient. We have used synthetic peptide combinatorial libraries to screen for hexapeptides that affect the recombination pathway at different stages, and have identified two families of peptides: one probably blocks DNA cleavage, the other may stabilize the Holliday junction intermediates. These peptides do not resemble parts of integrase or any of the other helper functions in the pathway. The deconvolution of hexapeptide libraries based both on inhibition of an enzymatic reaction as well as on accumulation of reaction intermediates is a novel approach to finding useful tools for dissecting a biochemical pathway.