Function of N² Methylguanine in Phenylalanine Transfer RNA

Abstract

ONE approach to determine the specific nucleotides primarily involved in the recognition of a tRNA by an aminoacyl tRNA synthetase is to compare the sequences of several tRNAs aminoacylated by a single synthetase and look for common nucleotides at specific sites. Using this approach we have compared the sequences of eight tRNAs of Table 1, all aminoacylated by yeast phenylalanyl tRNA synthetase^1–5 (PRS) and have proposed that the recognition site for this synthetase consists primarily of the nucleotides of the double stranded region adjacent to the dihydrouridine loop (diHU stem region) and adenosine at the fourth position from the 3′ end (Fig. 1)⁵. This conclusion was supported by the observation that tRNAs which have all of the boldface nucleotides of Fig. 1, but which lack either adenosine at position four, or the specific nucleotides of the diHU stem region, are not aminoacylated by PRS⁵. These observations demonstrated the absolute requirement for both the specific nucleotides of the diHU stem region and adenosine at position four from the 3′ end. Finally, this proposal is supported by chemical modifications of tRNAs amino-acylated by PRS^6–12 and by recent sequence determinations of tRNAs aminoacylated by PRS¹³, including Escherichia coil tRNA₁^Ala (R. Williams, W. Nagel, B. R., and B. D., in preparation).