DNA-REPLICATION INITIATES NON-RANDOMLY AT MULTIPLE SITES NEAR THE C-MYC GENE IN HELA-CELLS

The origin of replication of the c-myc gene in HeLa cells was previous ly identified at flow resolution within 3.5 kb 5' to the P-1 promoter, based on replication fork polarity and the location of DNA nascent st rands. To define the initiation events in the c-myc origin at higher r esolution the template bias of nascent DNAs in a 12 kb c-myc domain ha s been analyzed by hybridization to strand specific probes. Strong swi tches in the asymmetry of nascent strand template preference confirm t hat replication initiates non-randomly at multiple sites within 2.4 kb 5' to the c-myc P-1 promoter, and at other sites over a region of 12 kb or more. The strongest template biases occur in the 2.4 kb region 5 ' of the P-1 promoter, shown earlier to contain sequences which allow the autonomous semiconservative replication of c-myc plasmids. An asym metric pyrimidine heptanucleotide consensus sequence has been identifi ed which occurs 12 times in the c-myc origin zone, and whose polarity exactly correlates with the polarity of nascent strand synthesis.