Effect of tryptophan on informosomal and polyribosome-associated messenger RNA in rat liver

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.