**3. The role of estradiol in the nuclear entry of ERα**

Sai Padma et al (2000)and Sai Padma & Thampan(2000) observed that there were three nuclear proteins that contributed to the regulated entry of ERα into the nuclei. (a) the p55 that recognized the NLS on ERα(b)a 28kDa protein,p28 that bound to the NLS signal on ERα and thereby prevented the p55-ERα interaction;(c)a 73 kDa protein,p73 that bound to the hormone binding domain(HBD)on ERα.Under hormone free conditions,p28 remained bound to the ERα NLS,blocking the NLS recognition by p55.Estradiol binding to the HBD and the consequent conformational change in the HBD brought the HBD-bound p73 in close interaction with p28.This resulted in the dissociation of p28 from the NLS which was subsequently occupied by p55.The interaction culminated in the nuclear entry of ERα,also mediated by the cytoskeletal elements, actin and tubulin(14).
