The head genes of bacteriophage 21.

Physical and genetic maps of the head genes of lambdoid phage 21 have been made and compared with the head gene map of lambda. Because 21 and lambda have partial sequence homology throughout the head genes it was expected that the head genes of 21 would be analogous to those of lambda. Eight head genes of 21 have been identified and it was found that each of the genes is analogous in position, structure, and/or function to a lambda head gene. Phage 21 genes analogous to the lambda D and FI genes were not identified by mutation. Complementation studies between phage 21 and lambda mutants indicate that only gpFII (the protein product of a gene is referred to as gp (gene product] is fully interchangeable, gpW and gpD are partially interchangeable, and the rest of the head morphogenetic proteins are phage specific. In analogy with phage lambda, it is found that the gpNu3 analog (gp6) of phage 21 is synthesized from the same reading frame as the gpC analog (gp5), resulting in a protein identical to the carboxy terminus of gp5.