Genes 46 and 47 of phage T4: possible compensation for loss of their function.

The gene 46 and 47 functions of phage T4 are required for normal DNA replication, recombination, u.v. repair and host DNA breakdown, and yet am mutants defective in these genes characteristically form tiny plaques on Escherichia coli strains lacking an am suppressor. Our results imply that this limited growth is not due to misreading of am codons or partial function of nearly complete poly-peptides terminated at the am mutation. Thus it appears that genes 46 and 47 are not entirely essential, perhaps because other phage or host products can partially compensate for their loss.