The J gene of ϕX174: Isolation and characterization of a J gene mutant

The J gene protein of bacteriophage ϕX174 is a component of the mature phage. The previous lack of J gene mutants has prevented an in vivo analysis of J protein functions. A ϕX174 mutant was constructed by inserting an 11 nucleotide sequence into the J gene. This mutant, designated insJ, was viable only in the presence of a wild-type J gene carried on a plasmid that could provide J protein. An analysis of DNA synthesis during insJ mutant infection under non-permissive conditions confirmed that the J protein is not required for viral DNA synthesis.