Purification and properties of a translation inhibitor from wheat germ

Abstract

A translation inhibitor from wheat germ was purified more than 400-fold to apparent homogeneity. The inhibitor is a basic protein with a MW of 30,000. The protein effectively blocks protein synthesis in animal cell-free extracts [mouse brain, Ehrlich ascites cells and rabbit reticulocytes] but does not affect protein synthesis in intact cells. Inhibition occurs at a ribosome to inhibitor molar ratio of 100:1, indicating an enzymic mechanism of action. The wheat germ protein inhibits the translation of endogenous mRNA, exogenous mRNA and polyU at a step in polypeptide chain elongation and without breakdown of the polysomes. Neither the aminoacylation reaction nor mRNA degradation is affected by the inhibitor. The inhibition reaction requires the wheat germ inhibitor and both ATP and tRNA. The function of these 2 compounds in the inhibition is presently unknown; neither the hydrolysis of the .beta.,.gamma.-pyrophosphate bond of ATP nor a modification of the tRNA can be demonstrated during the reaction.