This family represents the phage-tail assembly chaperone proteins from a small set of Siphoviridae from Gammaproteobacteria. TACs are required for the morphogenesis of all long-tailed phages. The proposed function for the TAC is to coat the tape-measure protein to prevent it from forming unproductive complexes or precipitating before the tail tube protein has been incorporated [1].

1: 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