title: Occurrence of a 6S intermediate form of the progesterone receptor that is sensitive to ribonuclease.
abstract: Steroid receptors exist in cytosol as 9S, non-DNA-binding species and as 4S (transformed) species that bind to DNA or nuclei. Labeling the progesterone receptor from rabbit uterine cytosol with [3H]progesterone in the presence of 10 mM sodium molybdate revealed a 9S species on sucrose gradient centrifugation. Without molybdate, the receptor sedimented as an intermediate species of 6S, which converted to 4S in 0.3 M NaCl. The 6S species could also be generated from the 4S species by dialysis. Dilution of the same 4S species gave only partial re-aggregation with 50% of the receptor remaining as 4S. Dialysis appeared to retain the association of a macromolecular aggregation factor present in cytosol. Serum did not seem to be the source of the aggregation factor, as perfusion of the uterine vasculature before excision did not affect the S value of the receptor. We tested whether RNA was involved by treating receptor with RNase A (100 micrograms/400 microliters cytosol). While the molybdate-stabilized cytosol receptor (9S) was unaffected, RNase A partially (50%) converted the 6S form of receptor to 4S. RNase A also partially converted the re-aggregated form back to 4S. Protease inhibitors had no effect on this action of RNase. Formation of receptor-ribonucleotide protein particles may play a role in steroid action in the cell.
mesh_terms: D000818:Animals; D002499:Centrifugation, Density Gradient; D002852:Chromatography, Ion Exchange; D003600:Cytosol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D005260:Female; D012313:RNA / Q000378:metabolism*; D011817:Rabbits; D011980:Receptors, Progesterone / Q000032:analysis / Q000378:metabolism*; D012259:Ribonuclease, Pancreatic / Q000378:metabolism
chemical_list: D011980:Receptors, Progesterone; D012313:RNA; D004247:DNA; D012259:Ribonuclease, Pancreatic