Preparation of poly (A)-binding proteins from endoplasmic reticulum-containing subfractions of rat liver cells and their use in mRNA purification.

Approximately 2% of the proteins solubilised from rat liver microsomes or rapidly sedimenting endoplasmic reticulum (RS-ER) adsorbed to poly(A)-Sepharose. The adsorption appeared to be selective for a few proteins, and proteins of different apparent molecular weights adsorbed from RS-ER and the microsomes. The proteins from RS-ER with affinity for poly(A) were coupled to Sepharose and used for the purification of mRNA from rabbit mammary glands. A portion of the RNA wihich did not adsorb to poly(U)-Sepharose adsorbed to protein-Sepharose and was active in a cell-free protein synthesis system.