Isolation and characterization of a DNA primase from human mitochondria

A family of enzymatic activities isolated from human mitochondria is capable of initiating DNA replication on single-stranded templates. The principal enzymes include at least a primase and DNA polymerase gamma and require that rNTPs as well as dNTPs be present in the reaction mixture. Poly(dC) and poly(dT), as well as M13 phage DNA, are excellent templates for the primase activity. A single-stranded DNA containing the cloned origin of mitochondrial light-strand synthesis can be a more efficient template than M13 phage DNA alone. Primase and DNA polymerase activities were separated from each other by sedimentation in a glycerol density gradient. Using M13 phage DNA as template, these mitochondrial enzymes synthesize RNA primers that are 9 to 12 nucleotides in size and are covalently linked to nascent DNA. The formation of primers appears to be the rate-limiting step in the replication process. Replication of M13 DNA is sensitive to N-ethylmaleimide and dideoxynucleoside triphosphates, but insensitive to rifampicin, alpha-amanitin, and aphidicolin.