Age-dependent changes in the specificity of tRNA methyltransferases in the cerebellum of the icteric and nonicteric Gunn rat

Abstract

The activity of tRNA methyltransferases present in the cerebellum of 6- and 21-day-old nonicteric and icteric Gunn rats was compared using purified E. coli tRNAs as substrates. At 6 days the tRNA methyltransferases of the icteric animals were significantly more effective in methylating tRNA Glu 2 and tRNA Phe than were those of their nonicteric counterparts. This relationship reversed itself at 21 days. The action of the tRNA methyltransferases from the 6-day-old icteric animals led to higher proportions of 1-methyladenine in tRNA Glu 2 and tRNA Phe than were obtained using the corresponding enzymes of the nonicteric animals. The proportion of N 2 -methylguanine was also higher, yet only in tRNA fMet and not in tRNA Phe . The study reveals much more extensive fluctuations in the activity and in the substrate recognition specificity among the cerebellar tRNA methyltransferases of the icteric than among those of the nonicteric controls during the crucial 6–21 day period of cerebellar development.