Acts as a host protease inhibitor that allows the virus to initiate latency. Following infection, prevents protein cII degradation by inhibiting host protease FtsH (cII is a factor that initiates the expression of repressor cI, the major component promoting latency). Functions as a competitive inhibitor (and thus as alternative substrate) of host FtsH and thereby prevents binding of cII substrate. In turn, stabilization of cII transcriptional activator allows protein cI expression and thus initiation of latency. Belongs to the lambda phage cIII protein family. PubMed:6458018 assigned the gene cIII product to the sequence of the kil gene protein.