DNA Primase

DNA primase synthesizes small ribonucleotide primers for the initiation of DNA replication. The eukaryotic primase is a heterodimer of a small and a large subunit, p49 and p58 respectively. These two subunits purify as a complex tightly bound to DNA polymerase alpha. This tight association implicates polymerase alpha as the lagging-strand DNA polymerase in replication. Uniquely, primases are able to synthesize nucleotides de novo on a template by the formation of an initial dinucleotide. DNA primase initiates synthesis with a triphosphate purine moiety at the 5'-end. After synthesis of 7-10 ribonucleotides, the primer template is translocated intramolecularly to the active site of the DNA polymerase alpha subunit. The p49 subunit of DNA primase contains the catalytic active site. The human primase subunits are 90% identical in amino acid sequence to the mouse homologs.