No abstract

No abstract

The activity of the cII protein of phage A is probably the critical controlling factor in the choice of the lytic or lysogenic pathway by an infecting virus. Previous work has established that cIT activity is regulated through the turnover of cdi protein; the products of the hflA and hflB loci of Escherichia coli are needed for a degradative reaction, and A cI functions in stabilizing cdi. By using the cloned hflA locus, we have purified a cII-cleaving enzyme that we term ifiA. Purified HflA contains three polypeptides; at least two of the subunits are products of the hflA region, and the third is probably a cleavage product of the larger of these two hflAencoded polypeptides. The ifiA protease activity cleaves cdi to small fragments. We conclude that the switch between A developmental pathways involves regulated cleavage of cII by the specific protease ilfA.