CHARACTERIZATION OF THE ROUGH ENDOPLASMIC-RETICULUM RIBOSOME-BINDING ACTIVITY

THE rough endoplasmic reticulum membranes of mammalian cells contain specific ribosome-binding sites 1. A purification to apparent homogeneity of a negatively charged protein (ERpl80) of relative molecular mass 180,000 (180 K) was reported which was proposed to function as a rough endoplasmic reticulum ribosome receptor 2 We report here that ribosome-binding site activity quantitatively solubilized from rough endoplasmic reticulum membranes does not cofractionate with ERpl80. By contrast, ribosome-binding site activity fractionates as a much smaller, positively charged protein.