Purification and Properties of DNA Polymerases from Chick Embryo

Abstract

The main DNA polymerases present in cytoplasmic and nuclear soluble extracts of seven‐day‐old chick embryos have been purified. One of them, DNA polymerase I, mainly present in the cytoplasm has been obtained about 50–60% pure. Its molecular weight is 148 000 by Sephadex filtration and its s value is about 7.5S. This DNA polymerase is devoid of DNAase and RNAase activity. DNA polymerase II, of low molecular weight (50 000), sedimenting at 3 S, is the main DNA polymerase present in the nucleus and has been obtained 90% pure. The DNA polymerase II activity is also present in the cytoplasm. The purified cytoplasmic DNA polymerase II has a molecular weight of 27 000 and appears as a monomer of nuclear DNA polymerase II. The DNA polymerase II preparations, from either nucleus or cytoplasm, are devoid of nuclease activity and exhibit the same primer specificity; both are able to copy RNA strands in rAn· dTn hybrids whereas DNA polymerase I only copies the DNA strands in such hybrids.