Directed evolution of λ integrase activity and specificity by genetic derepression

Abstract

Advances in genome engineering are attendant on the development of novel enzyme variants with programed substrate specificities and improved activity. We have devised a novel selection method, wherein the activity of a recombinase deletes the gene encoding an inhibitor of an enzyme conferring a selectable phenotype. By using β-lactamase and the β-lactamase inhibitor protein, the selection couples recombinase activity to Escherichia coli survival in the presence of ampicillin. Using this method, we generated λ integrase variants displaying improved in vitro recombination of a non-cognate substrate present in the human genome. One generalist integrase variant displaying enhanced catalytic activity was further used in a facile, single-step transformation method to introduce transgenes up to 8.5 kb into the unique endogenous attB site of common laboratory E.coli strains.