Deletion mutants of bacteriophage phiX174.

Mutants of bacteriophage varphiX174 have been isolated that are less dense than wild-type varphiX particles in CsCl. When mutant viral (+) strand DNA and wild-type complementary (-) strand DNA are hybridized, the resulting duplex molecules have single-stranded loops characteristic of wild-type-deletion heteroduplexes. The mutant bacteriophages fail to complement varphiX amber mutants in cistron E. We conclude that the mutant viruses have deleted approximately 7% of the varphiX genome in the region of cistron E.