A bacterial protein requirement for the bacteriophage λ terminase reaction

Abstract
The bacteriophage lambda torminase enzyme cleaves the cohesive-end sites of λ DNA to yield the protruding 5'-termini of the mature molecule. In vitro, this ondonnclcolytic event requires a protein factor which has been isolated and purified from extracts of uninfected E. Coli. The terminase host factor (THF) is a heat stable basic protein of M.W. approximately 22, 000. The integration host factor (HIF) protein of E. Coli can efficiently substitute for THF in the terminase reaction; however, THF can be demonstrated to be physically present in, and isolated with full biological activity from extracts of cells defective or deficient in IHF.