Conversion of T4 gene 46 mutant deoxyribonucleic acid into nonviable bacteriophage particles.

The T4 amber mutant N130 in gene 46 produces, upon infection of a nonpermissive host, about 10 times more phage equivalent of deoxyribonucleic acid (DNA) than viable phage particles. Intracellular DNA is shorter than its mature phage counterpart and is converted into nonviable, light phage particles (287S) with about half of the normal DNA content, incapable either of adsorbing to or killing host bacteria. This DNA is highly unstable and breaks down, upon extraction, into subunits one-tenth the normal length of T4 DNA. Electron micrographs showed that the nonviable particles consist of normal-sized capsids of various degrees of fullness. Abnormal tail structures (naked cores with the sheaths missing) were also observed. Under conditions of arrested DNA synthesis, late messenger ribonucleic acid is produced, but some species are rare or missing, resulting in uneven transcription of the late genes. Our findings indicate that continuous DNA replication is necessary for normal transcription in T4.