title: Variation of DNA polymerase activities of rat giant trophoblast cells in mid-gestation.
abstract: The activities of the DNA polymerases alpha, beta, and gamma were determined in rat giant trophoblast cells during mid-gestation. Trophoblasts at this period of time have ceased to divide but continue to carry out DNA endoreduplication resulting in polyploidy. DNA polymerase-alpha activity in extracts was found to drop sharply from a high level at Day 11 to 1/10 of that level at Day 12 and to continue at a constant level thereafter. A similar pattern of activity was observed for polymerase-gamma, however, in this case the drop represented 50% of the activity at 11 days. Polymerase-beta showed no significant change in activity during this period of development. Endoreduplication (polyploidy) continued during this period as measured by a linear increase in chromosomal DNA content. The sharp drop in alpha-polymerase activity from Day 11 to Day 12 appears to result from the loss of a protein(s) which specifically stimulate(s) alpha-polymerase.
authors.affiliation: Department of Biochemistry, Jefferson Medical College of Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: G F
authors.initials: GF
authors.lastname: Kalf
authors.forename: R M
authors.initials: RM
authors.lastname: Metrione
authors.forename: B L
authors.initials: BL
authors.lastname: Kerlavage
authors.forename: T R
authors.initials: TR
authors.lastname: Koszalka
mesh_terms: D000818:Animals; D004247:DNA / Q000032:analysis; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D005260:Female; D005865:Gestational Age; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D014327:Trophoblasts / Q000201:enzymology*
chemical_list: D004247:DNA; D004259:DNA-Directed DNA Polymerase; D005033:Ethylmaleimide