1. 1) We have studied the early induction by oestradiol-17β, of the synthesis of specific proteins in the cytosol and chromatin fractions of the immature (19-21 days) rat uterus. Surviving uteri from rats given 5 ug of oestradiol-17β by intraperitoneal injection were incubated for l h with 3H-leucine; uteri from control rats were incubated with 14C-leucine. Corresponding fractions were pooled, and the 3H/14C ratio in electrophoretically separated protein components was determined. 2. 2) The oestradiol-17β-induced protein (IP) originally described by Gorski and Notides (1969) was found to be localized in the 106 g supernatant fraction of uteri homogenized in a medium which preserves the integrity of nuclei (0.25 M sucrose, 50 mM Tris buffer pH 7.5, 25 mM KCl and 5 mM MgCl2). No IP was found in liver from oestrogen-treated rats or in ovaries from rats treated with luteinizing hormone. 3. 3) IP was found to have a molecular weight of 39,000 by sodium dodecyi sulphate-poly-acrylamide gel electrophoresis and an isoelectric point of 4.5 as determined by isoelectric focusing in polyacrylamide gels. No evidence for phosphorylation of IP was obtained. 4. 4) Extraction of uterine chromatin with 6 M urea, 0.4 M guanidinium chloride, 0.1 M sodium phosphate, pH 7.0, followed by sodium dodecyi sulphate-polyacrylamide gel electrophoresis indicated the presence of at least three oestradiol-induced proteins with molecular weights of 42,000, 25,000 and 16,000 dalton respectively. The component of molecular weight 42,000 which is closest in size to IP was present in only small amounts. None of these components were piesent in liver from oestrogen-treated rats. 5. 5) Maximal amounts of the oestrogen-induced chromosomal proteins and of IP were found when the uteri were explanted 1 h after intraperitoneal injection of oestradiol-17β. 6. 6) None of the oestradiol-induced proteins in uterine chromatin were histones, as judged from their molecular weight, but the component of molecular weight 16,000 was basic, as indicated by its adsorption to Bio-Rex-70 ion exchange resin.
- induced protein
- protein synthesis