The DNA packaging enzyme terminase of bacteriophage lambda is a heteromultimer made up of the Nu1 and A genes. The small subunit, gpNu1, plays a crucial role in DNA recognition, while the large subunit, gpA, contributes to the late stages of packaging. During the initial packaging phases, terminase is involved in the site-specific binding and cleavage of DNA. This large subunit functions as an ATPase, which is necessary for the translocation of viral DNA into vacant capsids. Additionally, it functions as an endonuclease, cleaving the viral genome from the conidia to initiate and terminate the packaging reaction. The C-terminal domain, representing the nuclease/helicase, exhibits catalytic activity for DNA maturation.