Radiochemical Purification of Bacteriophage λ Integrase

Abstract

BACTERIOPHAGE λ has evolved a highly specific mechanism by which it integrates its DNA into the E. coli genome. The product of the lambda gene int, which I call integrase, mediates the insertion of the phage DNA at specific attachment sites on both the phage and host genomes^1–3. A non-enzymatic method by which integrase can be identified in infected cells has been described previously^4,5. It depends on the observation that in cells which have been heavily irradiated with ultraviolet light before infection with phage λ, synthesis of host proteins and most phage proteins is markedly depressed⁶. Under these conditions a high percentage of labelled amino acids is incorporated into phage-specific proteins including integrase. Using a differential labelling technique, integrase is identified by means of sodium dodecyl sulphate (SDS) gel electrophoresis as the only protein species eliminated by a nonsense (chain-terminating) mutation in the int gene.