In many tailed double-stranded DNA (dsDNA) virus such as Bacteriophage Sf6, the DNA newly synthesized is packaged into a preformed procapsid. The small subunit of the terminase is the component responsible for concatemeric viral DNA-recognition in the molecular machine that carries out this process. The small subunit of the terminase from phage Sf6, also known as gp1, consists of an N-terminal domain, a central alpha-helical domain and a C- terminal domain forming a beta-barrel, and adopts a ring-like octameric configuration composed of monomers [1,2].

1: Structural and functional studies of the phage Sf6 terminase small subunit reveal a DNA-spooling device facilitated by structural plasticity. Zhao H, Kamau YN, Christensen TE, Tang L; J Mol Biol. 2012;423:413-426. PMID:22858866

2: Crystal structure of the DNA-recognition component of the bacterial virus Sf6 genome-packaging machine. Zhao H, Finch CJ, Sequeira RD, Johnson BA, Johnson JE, Casjens SR, Tang L; Proc Natl Acad Sci U S A. 2010;107:1971-1976. PMID:20133842