Purification of a novel heat-stable translational inhibitor from rabbit reticulocyte lysates

July 1988 We have purified to apparent homogeneity a novel heat-stable (HS) factor from postribosomal supernatants of rabbit reticulocyte lysates by heating for IO min at 8O”C, fractionation on Sephadex, anion-exchange chromatography on QMA Accell, and gel filtration HPLC. The apparent molecular mass of HS is 50&1000 Da on the basis of its behaviour on gel filtration. Like a factor from bovine heart [(1982) Proc. Natl. Acad. Sci. USA 79, 31343137], the reticulocyte HS inhibits translation in hemin-supplemented lysates with biphasic kinetics similar to hemin deficiency and promotes phos- phorylation of the a-subunit of the eukaryotic initiation factor eIF-2. It is active at nanomolar concentrations. Reticulo- cyte HS appears to be neither a peptide nor an oligonucleotide since HS activity was insensitive to proteolytic or nucleo- lytic digestion. Polypeptide chain initiation; Translational inhibition; Protein phosphorylation; HPLC fractionation