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Effect of Tryptophan on Informosomal and Polyribosome-Associated Messenger RNA in Rat Liver^{1, 2,}

Department of Pathology, The George Washington University Medical Center, 2300 Eye Street, N.W., Washington, DC 20037

The possible role that informosomal mRNA may play in the stimulation of hepatic protein synthesis induced by the acute administration of tryptophan was investigated. L-tryptophan (30 mg/100 g body weight) tube-fed to rats induced an increase (20%) in the amount of polyribosome-associated poly(A⁺)mRNA in the liver within 1 hour. On the other hand, the amount of the informosomal poly(A⁺)mRNA revealed no significant increase or decrease. The size of the increase in the polyribosome-associated poly(A⁺)mRNA pool was equal to the entire amount of informosomal poly(A⁺)mRNA present in the hepatic cells. Therefore it was concluded that the failure to detect a significant decrease in the size of the informosomal mRNA pool indicated that the increase in the polyribosome-associated poly(A⁺)mRNA must be due to a different mechanism, such as enhanced nuclear-to-cytoplasmic translocation of nuclear poly(A⁺)mRNA, which had been reported earlier. To determine whether any qualitative or quantitative changes occurred in the RNA sequences along with the increase in poly(A⁺)mRNA following tryptophan administration, DNA/RNA hybridization studies were conducted by using hepatic polyribosome-associated poly(A⁺)mRNA from tryptophan-treated and control rats. Although qualitatively no new species of mRNA were detected in the mRNA from tryptophan-treated rats, kinetic analysis of the hybridization curves indicated that there was a shift or accumulation of hepatic poly(A⁺)mRNA belonging to the intermediate and possibly the high frequency classes of polyribosome-associated poly(A⁺)mRNA in the livers of the tryptophan-treated rats.

KEY WORDS: • tryptophan • poly(A⁺)mRNA • informosomal messenger ribonucleoprotein • DNA/RNA hybridization

¹ Supported by U.S. Public Health Service Research Grant AM 27339 from the National Institute of Arthritis, Metabolism and Digestive Diseases.

² A preliminary report was presented at the Meeting of the Federation of American Societies for Experimental Biology in Atlanta, GA, April, 1981, Fed. Proc. 40: 901, 1981.

Manuscript received 28 September 1984.