Identification of the tail assembly chaperone genes of T4-Like phages suggests a mechanism other than translational frameshifting for biogenesis of their encoded proteins.

Tape measure (TM) proteins are essential for the formation of long-tailed phages. TM protein assembly into tails requires the action of tail assembly chaperones (TACs). TACs (e.g. gpG and gpT of E. coli phage lambda) are usually produced in a short (TAC-N) and long form (TAC-NC) with the latter comprised of TAC-N with an additional C-terminal domain (TAC-C). TAC-NC is generally synthesized through a ribosomal frameshifting mechanism. TAC encoding genes have never been identified in the intensively studied Escherichia coli phage T4, or any related phages. Here, we have bioinformatically identified putative TAC encoding genes in diverse T4-like phage genomes. The frameshifting mechanism for producing TAC-NC appears to be conserved in several T4-like phage groups. However, the group including phage T4 itself likely employs a different strategy whereby TAC-N and TAC-NC are encoded by separate genes (26 and 51 in phage T4).