This family consists of Bacteriophage lambda minor tail protein G and related sequences [1]. The construction of phage tails involves a stage of tail-tube formation, and tail-tube polymerisation requires two additional proteins, gpG and gpGT. The open reading frames, ORFs, for gpG and gpGT are overlapping and are related by a programmed translational frameshift. During virion morphogenesis, gpG is expressed in large amounts, and about 3.5% of the time, a -1 translational frameshift leads to the production of the larger fusion protein, gpGT. The correct ratio of gpG to gpGT, as determined by the frequency of frameshifting, is crucial for tail assembly. Since gpG accumulates to high levels during a lambda infection and yet is not found in mature phage particles it is believed to act as a chaperone [2].

1: A programmed translational frameshift is required for the synthesis of a bacteriophage lambda tail assembly protein. Levin ME, Hendrix RW, Casjens SR; J Mol Biol 1993;234:124-139. PMID:8230192

2: A conserved spiral structure for highly diverged phage tail assembly chaperones. Pell LG, Cumby N, Clark TE, Tuite A, Battaile KP, Edwards AM, Chirgadze NY, Davidson AR, Maxwell KL; J Mol Biol. 2013;425:2436-2449. PMID:23542344