Normal human placentas contain RNA-directed DNA polymerase activity like that in viruses

J. Nelson, J. A. Leong, J. A. Levy

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51 Scopus citations


Extracts from over 100 normal human placentas have been examined for RNA-directed DNA polymerase (DNA nucleotidyltransferase, EC 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-like particles noted in the trophoblast layer of some human placentas.

Original languageEnglish (US)
Pages (from-to)6263-6267
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number12
StatePublished - 1978
Externally publishedYes

ASJC Scopus subject areas

  • General


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