BACTERIOPHAGE-T4 GENE-17 AMPLIFICATION MUTANTS - EVIDENCE FOR INITIATION BY THE T4 TERMINASE SUBUNIT GP16

Bacteriophage T4 genes 16 and 19 containing the 24 bp homology regions that recombine to form Hp17 mutants were cloned into plasmids. When t he two homology sequences were cloned either together into one or sepa rately into two compatible plasmids, a polymerase chain reaction assay showed that recombination occurred in vivo. The recombinant sequence was identical with that found in T4 phage Hp17 mutants, and was produc ed in recombination-deficient Escherichia coli. Mutational analysis re vealed a requirement for functional gene 16 but not gene 17 to recombi ne the sequences. Moreover, gp16, the terminase small Subunit, was req uired, since an amber gene 16 produced the recombinant sequence only w hen suppressed. Mutations in the gene 16 recombination sequence (3GA a nd 15TG) that eliminated Hp17 formation in T4 phage increased the synt hesis of the large terminase subunit, gp17 in T4 infections, suggestin g gp16 interaction with this site, gp16 binding to gene 16 and gene 19 pac-like sites may synapse the homologous sequences to lead to Hp17 m utant formation, and this suggests a synapsis mechanism for control of T4 DNA maturation and concatemer processing in packaging.