THE INTERACTION OF SYNTHETIC TEMPLATES WITH EUKARYOTIC DNA PRIMASE

The template interaction of calf thymus and human placenta DNA primase s has been investigated. Using oligothymidylates, we showed that a tem plate consisting of ten monomeric units was the critical size for inte raction with the enzyme. The hydrophobic effect is likely to be a majo r factor determining template recognition by the DNA primase. The corr elation between the template affinity with the enzyme and the octanol- water hydrophobic scale confirms this suggestion. In addition, the ele ctrostatic interaction between the phosphate group of the template and side chains on the enzyme probably increases template affinity. Using methylated poly(dA), we found that the first nucleotide base of the p rimer should be more hydrophobic than the corresponding nucleotide bas e of the template. A model for the mechanism of action of DNA primase is suggested on the basis of data presented in this study and previous findings. According to this model, (a) DNA primase binds ten nucleoti des of the template; (b) the synthesis of primer up to the formation o f a decamer occurs processively and competes with template binding of the enzyme; (c) the conditions under which the nucleotides are incorpo rated into the RNA product change during the extension of the primer, and these changes are responsible for switching from primase to polyme rase activity. The template specificity of DNA primase is likely to pl ay an important role in the initiation and regulation of DNA replicati on.