Localization and topology of ratp28, a member of a novel family of putative steroid-binding proteins

We have cloned ratp28, a membrane protein from rat liver homologous to the previously described hpr6.6, a putative steroid-binding protein in humans. Ratp28 has a type II topology as determined by protease digestion experimen ts on intact and detergent-solubilized membranes. Subcellular fractionation by sucrose density centrifugation revealed a distribution for ratp28 ident ical to Bip as a marker for membranes of the endoplasmic reticulum. In thes e experiments no association was found with markers for Golgi or plasma mem branes, indicating that ratp28 is localized to the endoplasmic reticulum. ( C) 2000 Elsevier Science B.V. All rights reserved.