This small family of phage proteins are bound in the viral membrane and assist, along with P11 and P18 in the delivery of DNA [1].

1: A snapshot of viral evolution from genome analysis of the tectiviridae family. Saren AM, Ravantti JJ, Benson SD, Burnett RM, Paulin L, Bamford DH, Bamford JK; J Mol Biol. 2005;350:427-440. PMID:15946683