Abstract
DNA synthesis in vitro was studied in rat giant trophoblast nuclei from parietal yolk sacs at Day 13 of development. These nuclei synthesize DNA by a series of endoreduplications in the absence of mitosis. Although the nuclei contain DNA polymerase alpha and beta activities, polymerase alpha activity is not expressed since DNA synthesis is insensitive to aphidicolin. In contrast, N-ethylmaleimide and the DNA polymerase beta inhibitors, 50 mM potassium phosphate, and 2',3'-dideoxythymidine triphosphate inhibit DNA synthesis in isolated nuclei to a degree identical with that seen with partially purified trophoblast DNA polymerase beta, suggesting that polymerase beta is the major polymerase activity in Day 13 trophoblast nuclei. DNA synthesis by these nuclei is dependent on ATP and inhibited by novobiocin and has been shown to be replicative rather than repair-type synthesis, since the newly synthesized DNA is contiguous with DNA replicated in vivo in the presence of a bromodeoxyuridine density label. The results suggest that DNA endoreduplication in these nuclei is being carried out by DNA polymerase beta.
Highlights
DNA synthesis in vitro was studied in rat giant tro- of DNApolymerase y is to replicate mitochondrial DNA
The product of nuclear DNA synthesis was seen to be very sensitive to DNase I treatment or pretreatment of the nuclei by heating to 50 "C for 10 min
It may be observed that DNA synthesis appears to be low in relation to other reported nuclear systems, e.g. HeLa cell nuclei [22]
Summary
DNA synthesis in vitro was studied in rat giant tro- of DNApolymerase y is to replicate mitochondrial DNA. Phoblast nuclei from parietal yolk sacs at Day of these assignments are generally accepted, they are development. These nuclei synthesizeDNA by a series not exclusive of other functions. Data presented supof endoreduplications in theabsence of mitosis.Al- port the involvement of DNA polymerasep in the endoreduthoughthenucleicontain DNA polymerase a and p plication of DNA introphoblast cells at Day 13 of pregnancy. N-ethylmaleimide and the DNA polymerase B inhibitors, 50 m~ potassiumphosphate, and2‘,3’-dideoxy-
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