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

Abstract We have purified to apparent homogeneity a novel heat-stable (HS) factor from postribosomal supernatants of rabbit reticulocyte lysates by heating for 10 min at 80°C, fractionation on Sephadex, anion-exchange chromatography on QMA Accell, and gel filtration HPLC. The apparent molecular mass of HS is 500–1000 Da on the basis of its behaviour on gel filtration. Like a factor from bovine heart [(1982) Proc. Natl. Acad. Sci. USA 79, 3134–3137], the reticulocyte HS inhibits translation in hemin-supplemented lysates with biphasic kinetics similar to hemin deficiency and promotes phosphorylation of the α-subunit of the eukaryotic initiation factor eIF-2. It is active at nanomolar concentrations. Reticulocyte HS appears to be neither a peptide nor an oligonucleotide since HS activity was insensitive to proteolytic or nucleolytic digestion.