Isolation from calf brain of a polypeptide fraction affecting aminoacylation of tRNA

The preparation of tRNA obtained from calf brain by three conventional methods exhibits the presence of a slow-migrating fraction in polyacrylamide-gel electrophoresis. This fraction constitutes 2-2.5% of the isolated tRNA and has been identified as a polypeptide of molecular weight of 6000. The aminoacylation with glutamic acid, glycine, leucine and phenylalanine of tRNA devoid of this polypeptide is reduced by half as compared with the initial preparation.