BACTERIOPHAGE-T4 INITIATES BIDIRECTIONAL DNA-REPLICATION THROUGH A 2-STEP PROCESS

Two-dimensional gel analysis of the bacteriophage T4 ori(uvsY) region revealed a novel ''comet'' on the Y are. This comet contains simple Y molecules in which the branch points map to the ori(uvsY) transcript r egion. The comet depends on the the origin and DNA synthesis and is ab olished by a mutation that reduces replication without affecting trans cription. These results argue that the branched molecules are intermed iates in replication initiation. A transcriptional terminator, cloned just downstream of the origin promoter, shortened the tail of the come t. Therefore, the location of the transcript determines the DNA branch points. We conclude that the comet DNA consists of intermediates in w hich unidirectional replication has been triggered by priming from the RNA of the origin R loop.