title: Amber mutants of bacteriophages T3 and T7 defective in phage-directed deoxyribonucleic acid synthesis.
abstract: Amber mutants of the related phages T3 and T7 were isolated and tested for their ability to restore-as the wild type does-thymidine incorporation in ultraviolet (UV)-irradiated, UV-sensitive, nonpermissive host bacteria (Escherichia coli B(s-1)). Most amber mutants had this ability. However, in both T3 and T7, mutants unable to promote thymidine incorporation under these conditions were found and classified into two well-defined complementation groups: T3DO-A and T3DO-B, T7DO-A and T7DO-B. Infection of B(s-1) cells with representatives of groups DO-A had the following characteristics: (i) phage-directed uridine uptake in UV-irradiated cells was reduced to less than 20% of normal; (ii) breakdown of host deoxyribonucleic acid (DNA) was delayed and incomplete; (iii) no serum-blocking antigens appeared; (iv) no cell lysis occurred; (v) the ability to exclude the heterologous wild type was impaired. Amber mutants of the DO-B groups, infecting B(s-1), were able to: (i) promote an efficient phage-directed uridine uptake in UV-irradiated cells; (ii) bring about rapid breakdown of host DNA; (iii) synthesize serum-blocking antigens; (iv) lyse the host cells, generally after the normal latent period; (v) exclude efficiently the heterologous wild type. Although physiological similarities between the respective DO-A mutants or DO-B mutants of T3 and T7 were evident, no physiological cross-complementation occurred, and genetic crosses gave no evidence of genetic homologies between groups of T3 and T7.
mesh_terms: D001433:Bacteriolysis; D003090:Coliphages / Q000378:metabolism; D003433:Crosses, Genetic; D004269:DNA, Bacterial / Q000096:biosynthesis*; D004279:DNA, Viral / Q000096:biosynthesis; D004926:Escherichia coli / Q000378:metabolism* / Q000528:radiation effects; D005827:Genetics, Microbial; D009154:Mutation; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014466:Ultraviolet Rays; D014529:Uridine / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D004279:DNA, Viral; D014316:Tritium; D013936:Thymidine; D014529:Uridine