DNA-directed and RNA-primed DNA synthesis in microsomal and mitochondrial fractions of normal human lymphocytes

Abstract

Nascent DNA synthesized from RNase-sensitive endogenous DNA polymerase activities of microsomal and mitochondrial fractions from phytohemagglutinin-stimulated normal human blood lymphocytes is covalently attached to a small RNA molecule (<4S in the case of the microsomal fraction). This complex is in turn originally hydrogen bonded to a much larger preexistent DNA molecule, indicating that this synthesis of DNA is directed by DNA (template) and that the RNA is utilized solely as an initiator molecule (primer). This endogenous RNase-sensitive DNA synthesis should not be confused with the endogenous RNase-sensitive DNA synthesis in type-C RNA tumor viruses and in related cytoplasmic particles from human leukemic cells catalyzed by reverse transcriptase which utilizes RNA as both template and primer. These findings are consistent with the concept that some DNA synthesis in mammalian cell organelles may be analogous to that of bacteria in utilizing RNA primers with DNA templates.