Localization of estrogen receptor regulatory factor in the uterine nucleus

The objective of this study was to determine whether progesterone-induced estrogen receptor regulatory factor (ReRF) is a component of hamster uterine nuclei or a cytoplasmic contaminant of the nuclear fraction. Crude uterine nuclei were prepared in low salt buffer and were purified by either the hexylene glycol method or an isotonic sucrose-Triton X-100 procedure. ReRF activity was measured as a net percentage increase in estrogen receptor inactivation after incubation of a 0.5 M KCl nuclear extract at 36 degrees C for 30 min. Progesterone treatment (5 mg/kg, s.c. in oil, 2 h) increased net receptor inactivation to the same extent (9-12% net increase) in extract made from each nuclear preparation. Extensive washing of nuclei caused a progressive decline in recovery of ReRF activity, in parallel with the behavior of KCl-extractable nuclear protein and estrogen receptor. These results demonstrate that ReRF is a loosely bound component of the uterine nucleus.