Renaturation of rabbit liver aminoacyl-tRNA synthetases by 80S ribosomes.

Protein biosynthesis machinery is thought to be mostly compartmentalised wi thin the mammalian cell, involving direct interactions between different co mponents of the translation apparatus. The present research concerns the fu nctional meaning of the interaction between the rabbit liver aminoacyl-tRNA synthetases and 80S ribosomes. We have shown that rabbit liver 80S ribosom es are able to enhance the activity of leucyl-tRNA synthetase, which is a c omponent of high-molecular weight aminoacyl-tRNA synthetase complex, and ph enylalanyl-tRNA synthetase not associated within this complex. The ribosome s increase the initial rate of both the total reaction of tRNA aminoacylati on and the first step of this reaction, the formation of leucyladenylate. M oreover. a positive cooperativity of the tRNA interaction with two binding sites of leucyl-tRNA synthetase is also increased in the presence of highly purified 80S ribosomes. The effect of 80S ribosomes on partly denatured leucyl-tRNA synthetase and phenylalanyl-tRNA synthetase and the protection by 80S ribosomes of both en zymes against inactivation indicate a refolding and stabilising capacity of the ribosomes. It is concluded that the interaction of aminoacyl-tRNA synt hetases and 80S ribosomes is important for the maintenance of an active con formation of the enzymes. (C) 1999 Elsevier Science Ltd. All rights reserve d.