title: Normal human placentas contain RNA-directed DNA polymerase activity like that in viruses.
abstract: Extracts from over 100 normal human placentas have been examined for RNA-directed DNA polymerase (DNA nucleotidyltransferase, EC 2.7.7.7) activity. More than 80% of these placentas contained this enzyme activity, which banded at a density of 1.15-1.17 g/ml in sucrose. After heat treatment, this enzyme activity was shifted in density to 1.22-1.24 g/ml. The enzymatic activity was greater with (rC)n.(dG)12-18 than with (dC)n.(dG)12-18 and was not stimulated by (dG)12-18 alone. The product of the endogenous reaction, which was sensitive to RNase, had the characteristics of a small DNA associated with a large RNA by hydrogen bonding. Electron microscopic inspection of the material with a density of 1.15-1.17 g/ml revealed numerous retrovirus-like particles with central electron-dense cores and double-membraned envelopes. The enzyme may be associated with the retrovirus-lik particles noted in the trophoblast layer of some human placentas.
mesh_terms: D005260:Female; D006801:Humans; D007181:Inclusion Bodies, Viral / Q000648:ultrastructure; D010920:Placenta / Q000201:enzymology* / Q000382:microbiology / Q000648:ultrastructure; D011247:Pregnancy; D012194:RNA-Directed DNA Polymerase / Q000378:metabolism*; D012260:Ribonucleases / Q000378:metabolism
chemical_list: D012194:RNA-Directed DNA Polymerase; D012260:Ribonucleases