Acts as a transcriptional repressor that allows virus to establish and maintain latency. Prevents both the viral DNA replication and the exit programs. Clamps the two operator OL (operator left made of OL1, OL2 and OL3 sites) and OR (operator right made of OR1, OR2 and OR3 sites) together by binding to them and arranging the intervening DNA in a loop. This step allows repression of lytic pR and pL promoters by binding to OL1, OL2, OR1 and OR2 simultaneously. The binding of cI on OR2 additionally activates the transcription of the cI gene thereby mediating an autoregulatory function to maintain the latent state. Once cI is present in sufficient amount, it can repress its own transcription by binding to OL3 and OR3. Homooctamer. The DNA loop is maintained by octamers of repressor cI. Bacterial cells harboring a lysogenic lambda phage are immune to further infection by lambda. The cI repressor protein inhibits the lytic development of any additional infecting phage particles. The region of the genome that codes for the cI repressor protein is known as the immunity region.