Hybridization mapping of restriction fragments from the early region of bacteriophage T7 DNA

Abstract

By hybridizing individual early RNA species from T7-infected cells to HpaI cleavage products of T7 DNA, we have identified the fragments which comprise the early region of the T7 genome and have deduced their order with respect to the genetic and physical maps. From the left end of the DNA molecule the arrangement of HpaI DNA fragments is: F·H·G·Q. Our results indicate that the termination signal for the host RNA polymerase is situated in, or near the right end of, HpaI fragment Q (at about 19.3% of the genome). In vivo, recognition of the termination signal at the end of the early region by the host RNA polymerase occurs with about 70–75% efficiency. Late mRNA from T7-infected cells was also analyzed by this technique. Our results demonstrate that both class II and class III genes are efficiently transcribed during the interval from 6 to 12 min after infection. These results are contrasted with those observed for the purified phage RNA polymerase in vitro.