Transfer ribonucleic acid-dependent but ribosome-independent leucine incorporation into rat brain protein

Abstract

An unusual type of posttranslational modification was observed in a rat brain in vitro system. It consists in leucine addition to a performed protein in such a way that the added leucine is located at neither the NH2 nor the COOH terminus of the acceptor protein. The incorporation reaction requires ATP, ATP-generating components and tRNA. It is inhibited by aurintricarboxylic acid but does not require the presence of ribosomes or GTP. The incorporated leucine has a free NH2 group, and it is not released by leucine aminopeptidase or carboxypeptidase A. It is linked to the acceptor protein through a bond that is too alkali labile and too hydroxylamine labile to be a peptide bond. The simplest interpretation of the results consists in proposing that an ester bond is formed between the leucine and the side chain of a serine, threonine or tyrosine in the acceptor protein.