Identification of the ‘estrogen-induced protein’ in uterus and brain of untreated immature rats

Abstract

The appearance of a specific estrogen-induced protein (IP) in the rat uterus [l] represents one of the earliest effects of estrogen on uterine macromolecular synthesis [2]. This effect can be reproducibly demonstrated following in vitro as well as in vivo estrogen treatment (3-S], making IP the most convenient marker protein available for studying the mechanism of action of estrogen in the rat uterus. IP has been routinely detected using a doubleisotope ratio method [6]. This method is convenient, but it cannot yield information on content or rate of synthesis of IP in non-treated organs, or in organs in which IP may be present but not susceptible to induction by estrogen. We have reported initial results, on the time course and age dependence of IP induction [7], using ~uoro~aphy of ~35S]met~on~e-labelled proteins separated by sodium dodecyl sulfate polyac~l~ide gel electrophoresis [S]. We describe here the characterization of IP by partial protease digestion, which enables the identification of IP as a major constitutive protein in uterus,pituitary, hypothalamus and cerebral cortex of immature rats. (A short report of some of these findings was presented [9] .)