This family represents the protease responsible for the proteolysis of head proteins, a critical step in the morphogenesis of many tailed phages, Cleavage facilitates the conversion of the prohead to the mature capsid. All these cleavages are carried out by action at consensus S/A/G-X-E recognition sequences at 39 cleavage sites. Evidence of multiple processing sites in nine phiKZ proteins appears to represent a built-in mechanism by which the phage ensures that the majority of the propeptide regions are removed, and emphasizes the essential nature of processing in phiKZ-head morphogenesis [1]. The family is classified by MEROPS as a serine peptidase.

1: Extensive proteolysis of head and inner body proteins by a morphogenetic protease in the giant Pseudomonas aeruginosa phage phiKZ. Thomas JA, Weintraub ST, Wu W, Winkler DC, Cheng N, Steven AC, Black LW; Mol Microbiol. 2012;84:324-339. PMID:22429790