The terminase small subunit specifically recognizes the non-adjacent pacL and pacR packaging subsites and regulates the ATPase activity of the terminase large subunit. 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 (packaging sequence), and a large terminase subunit possessing endonucleolytic and ATPase activities. Both terminase subunits heterooligomerize and are docked on the portal protein to form the packaging machine. The terminase large subunit exhibits endonuclease activity and cleaves the viral genome concatemer once the capsid is full (headful packaging). Once the capsid is packaged with the DNA, the terminase complex is substituted by neck proteins. Homononamer. Interacts with the terminase large subunit gp2; the active complex is probably composed of a one monomer of gp2 and two or more nonamers of gp1. Belongs to the SPP1-like small terminase family.