Cloning and sequencing of the genetic right end of bacteriophage T3 DNA

The genetic right end of phage T3 DNA, from the beginning of gene 17, was cloned and sequenced. Genes 17, 18, and 19 were identified by comparing the sequence with the genetic map and by comparing the calculated and observed molecular weights of gene products. N-terminal amino acid sequence of the gene 17 product (gp17) predicted from the nucleotide sequence was consistent with the data from the analysis of purified gp17. Gene 17.5 was identified as the lysis gene on the basis of the presence of a nonsense codon within an open reading frame in the sequence of DNA from an amber mutant of lysis gene. In addition, five potential genes have been identified. Sequences corresponding to a promoter for phage T7 RNA polymerase (Rosa and Andrews, 1981) and to a class-III promoter for phage T3 RNA polymerase (Sarker et al., 1985) were found. The genomic organization and the nucleotide and deduced amino acid sequences of T3 were compared with those of T7. The genomic organizations of T3 and T7 were identical in this region. The sequence comparisons of T3 and T7 DNA point out the highly conserved sequences in all genes but also heavily varied regions in some genes. From these comparisons, possible implications with regard to structural and functional domains within several genes are discussed.