EUKARYOTIC DNA PRIMASE DOES NOT PREFER TO SYNTHESIZE PRIMERS AT PYRIMIDINE RICH DNA-SEQUENCES WHEN NUCLEOSIDE TRIPHOSPHATES ARE PRESENT AT CONCENTRATIONS FOUND IN WHOLE CELLS

The critical role of NTP concentration in determining where calf thymu s DNA primase synthesizes a primer on a DNA template was examined. Var ying the concentration of NTPs dramatically altered the template seque nces at which primase synthesized primers. At the low NTP concentratio ns typically used for in vitro experiments (100 mu M), primase greatly preferred to synthesize primers at pyrimidine rich DNA sequences. How ever, when the concentrations of NTPs were increased to levels typical ly found in whole cells, primers were now synthesized in all regions o f the template. Importantly, synthesis of primers in all regions of th e DNA template, not just the pyrimidine rich sequences, is the pattern of primer synthesis observed during DNA replication in whole cells. W ith low concentrations of NTPs (i.e., V-max/K-M conditions), primers a re only synthesized at the most preferred synthesis sites, namely, tho se that are pyrimidine rich. In contrast, under conditions of high NTP concentrations, primer synthesis will occur at the first potential sy nthesis site to which primase binds. Now, the primase DNA complex will be immediately converted to a primase DNA NTP NTP complex that is poi sed for primer synthesis.