Acts as a transcriptional activator that allows virus to initiate a latent state. Following infection, participates, together with cIII, in activation of the Pe and Pi promoters, which are responsible for the transcription of the cI (repressor) and int (integrase) genes, respectively. Both of these gene products are required for the establishment of latency. Homotetramer. Interacts with cIII; this interaction is essential to stabilize cII that would otherwise be quickly degraded by host protease FtsH. Lambda-imm434 is a hybrid of bacteriophages 434 and lambda. The cII protein coding region is in the lambda portion of the imm434 genome. Belongs to the lambda phage cII protein family.