DNA polymerase gamma has been purified over 60 000-fold from HeLa cells which contain no detectable type C viral particles. This purified enzyme shows a specific activity of 25 000 units/mg of protein which is comparable to the known specific activity of homogeneous preparations of human alpha and beta polymerases. The isolated enzyme shows apparent molecular weights ranging from 160 000 to 330 000 according to the method of analysis. The enzyme exhibits optimal activity for copying poly(A) in the presence of 50 mM KPO4 and 130 mM KCl and, under these conditions, copies poly(A) 20 times more rapidly than activated DNA. These assay conditions permit a clear distinction between the gamma-polymerase and DNA polymerase beta which is markedly inhibited by phosphate at this concentration. A comparison of the copying of activated DNA, poly(dA) and poly(A) by DNA polymerases alpha, beta, and gamma under optimal assay conditions for each enzyme is presented. Studies with synthetic and natural nucleic acid templates also show the gamma-polymerase to behave differently that the reverse transcriptases of avian myeloblastosis virus or Rauscher leukemia virus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.