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Abstract:
The RF† DNAs of bacteriophages fd, f1 and M13 are cleaved by nuclease Hpa II at 13 sites. As compared to fd RF DNA, f1 and M13 RF DNA have one cleavage site in a different position. DNA fragments were ordered by using fragments as primers for the in vitro synthesis of their neighbours. The resulting physical map was correlated with the genetic map by marker rescue experiments with amber mutant phage DNAs and purified wild-type DNA fragments (Hutchison et al., 1971).
RNA polymerase binding sites were detected in six of the 13 Hpa II fragments. Each site promotes the synthesis of RNA, with four species being initiated fay GTP and two by ATP. The sites display different affinities for the enzyme and are distributed throughout the genome. A site that is occupied preferentially by the enzyme is located at the distal end of gene II near a unique site on the genome where all phage RNA species seem to be terminated. It promotes the synthesis of RNA from a region of the genome that is expressed very actively in vivo. In view of these findings, a mechanism for constitutive transcriptional control is proposed.
