Enzymatic breakage of the cohesive end site of phage lambda DNA: terminase (ter) reaction.

An in vitro system is described for measuring the endonucleolytic conversion of the phage lambda cohesive end sites in concatemeric DNA to the cohesive chromosomal ends of the mature molecule. This enzymic process, known as the ter reaction, is catalyzed by purified lambda A gene protein. The reaction is markedly stimulated by ATP, Mg2+, spermidine, and one or more uncharacterized factors present in extracts of uninfected Escherichia coli cells. In vitro, the ter reaction proceeds in the absence of proheads under conditions that are similar to those previously found necessary for the formation of a DNA-A gene protein intermediate for the initiation of packaging.