The small subunit is responsible for the binding to multiple recognition elements within the packaging initiation site cos (PubMed:15755448, PubMed:16618107, PubMed:2989542). The terminase lies at a unique vertex of the procapsid and is composed of two subunits, a small terminase subunit involved in viral DNA recognition (binding to packaging sequence cos), and a large terminase subunit possessing endonucleolytic, ATPase and helicase activities (DNA maturation and packaging) (Probable). The terminase binds, cooperatively with the host factor IHFA/IHFB, to the cos site at the junction of adjacent viral genomes in the concatemeric DNA (PubMed:16618107). The endonuclease and helicase activities of the large subunit cleave the viral DNA generating 5'overhangs of 12 bp in length (Probable). The terminase remains bound to the left end of the genome to be packaged, forming a stable DNA-terminase complex (Probable). In a reaction facilitated by the viral assembly catalyst gpFI, the DNA-terminase complex binds to the portal of the procapsid and the terminase packages the viral DNA into the procapsid until the next cos site on the concatemer reaches the complex (Probable). The downstream cos site is then cut generating the mature right end of the genome, the heterotrimer undocks from the DNA-filled head and remains bound to the left end of concatemer's next genome (Probable). ATP + H2O = ADP + H(+) + phosphate Heterotrimer of two small and one large terminase subunits (PubMed:15755448). The catalytically competent terminase is composed of a tetramer of heterotrimers (PubMed:30541105, PubMed:16618107). The tetramer forms a ring structure large enough to encircle duplex DNA (PubMed:30541105). Host IHFA/IHFB induces bending of viral DNA to facilitate the assembly of the terminase tetramer of heterotrimers (PubMed:16618107). Interacts (via C-terminus) with the terminase large subunit (via N-terminus) (PubMed:2969839). The terminase lies at a unique vertex of the procapsid during viral DNA packaging. The N-terminus contains a winged helix-turn-helix (wHTH) that binds the viral DNA (PubMed:12049735) (Probable). The N-terminus also contains an ATPase site that regulates DNA binding activity (PubMed:9705918, PubMed:2965248, PubMed:16008350). The central part contains a region for the self-interaction (PubMed:10571997). the C-terminus contains region of interaction with the terminase large subunit (PubMed:10571997) (Probable). Belongs to the terminase small subunit family.