This family consists of several bacteriophage capsid scaffolding proteins (GPO) and some related bacterial sequences. GPO is thought to function in both the assembly of proheads and the cleavage of GPN [1]. The family is found to function as a serine peptidase, with a conserved Asp, His and Ser catalytic triad, as in subtilisin, and as represented in MEROPS:S73. The family includes SwissProt:P25478 from Enterobacteria phage P2 which cleaves itself and then becomes the scaffold protein upon which the bacteriophage prohead is built - a mechanism quite common amongst phages [2].

1: Nucleotide sequence of the DNA packaging and capsid synthesis genes of bacteriophage P2. Linderoth NA, Ziermann R, Haggard-Ljungquist E, Christie GE, Calendar R; Nucleic Acids Res 1991;19:7207-7214. PMID:1837355

2: Functional domains of the bacteriophage P2 scaffolding protein: Identification of residues involved in assembly and protease activity. Chang JR, Spilman MS, Rodenburg CM, Dokland T; 2008; [Epub ahead of print] PMID:19064277