Identification of some steps in the replication of bacteriophage T1 DNA

Abstract

The effects of amber mutations in the 25 known genes of phage T1 on phage DNA replication were examined by sedimentation analysis of pulse-labelled DNA extracted from infected nonpermissive cells. Five groups of mutants were identified according to their DNA phenotype. Group I comprises am20 (gene 1) and am5 (gene 2) which are totally defective in DNA synthesis as previously shown by D. Figurski and J. R. Christensen (1974, Virology 59, 397–407). Group IIA also consists of two mutants, am201 (gene 3.5) and am23 (gene 4), both of which fail to make concatemeric DNA. Group II includes am41(gene 3), am15 (gene 5), am18 (gene 6), am35 (gene 7), am32 (gene 8), am13 (gene 9), am19 (gene 10), am29 (gene 11), am304 (gene 11.5), and am37 (gene 12). This group, represented predominantly by genes controlling tail formation, exhibits a wild-type pattern in which concatemerie DNA is synthesized and then processed to unit-length molecules. Group III mutants are all defective in head formation and accumulate concatemeric DNA molecules. This group contains am10 (gene 13), am216 (gene 13.7), am45 (gene 14), am246 (gene 14.5), am11 (gene 15), am4 (gene 16), am7 (gene 17), and am30 (gene 18). Group IV is represented by a single mutant, am283 (gene 13.3), with a sedimentation pattern intermediate between that of Group II and Group III mutants. It is not known if am283 is defective in concatemer formation or concatemer processing.