{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,21]],"date-time":"2026-05-21T09:14:10Z","timestamp":1779354850685,"version":"3.51.4"},"reference-count":0,"publisher":"Proceedings of the National Academy of Sciences","issue":"12","content-domain":{"domain":["www.pnas.org"],"crossmark-restriction":true},"short-container-title":["Proc. Natl. Acad. Sci. U.S.A."],"published-print":{"date-parts":[[1978,12]]},"abstract":"<jats:p>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.<\/jats:p>","DOI":"10.1073\/pnas.75.12.6263","type":"journal-article","created":{"date-parts":[[2006,5,31]],"date-time":"2006-05-31T07:38:20Z","timestamp":1149061100000},"page":"6263-6267","update-policy":"https:\/\/doi.org\/10.1073\/pnas.cm10313","source":"Crossref","is-referenced-by-count":49,"title":["Normal human placentas contain RNA-directed DNA polymerase activity like that in viruses."],"prefix":"10.1073","volume":"75","author":[{"given":"J","family":"Nelson","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"J A","family":"Leong","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"J A","family":"Levy","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"341","published-online":{"date-parts":[[1978,12]]},"container-title":["Proceedings of the National Academy of Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pnas.org\/doi\/pdf\/10.1073\/pnas.75.12.6263","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2022,4,13]],"date-time":"2022-04-13T15:09:27Z","timestamp":1649862567000},"score":1,"resource":{"primary":{"URL":"https:\/\/pnas.org\/doi\/full\/10.1073\/pnas.75.12.6263"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[1978,12]]},"references-count":0,"journal-issue":{"issue":"12","published-print":{"date-parts":[[1978,12]]}},"alternative-id":["10.1073\/pnas.75.12.6263"],"URL":"https:\/\/doi.org\/10.1073\/pnas.75.12.6263","relation":{},"ISSN":["0027-8424","1091-6490"],"issn-type":[{"value":"0027-8424","type":"print"},{"value":"1091-6490","type":"electronic"}],"subject":[],"published":{"date-parts":[[1978,12]]},"assertion":[{"value":"1978-12-01","order":2,"name":"published","label":"Published","group":{"name":"publication_history","label":"Publication History"}}]}}