Loss of methyl acceptor activity of ultraviolet-irradiated tRNA

Abstract

THE features responsible for the recognition of specific sites for methylation by tRNA methylases are presently not understood. Studies by Kuchino and Nishimura suggest that a specific octanucleotide sequence is recognised by rat liver guanosine methylases¹. Furthermore, reports from Nishimura's laboratory show that a large (three-quarter) fragment from E. coli methionine tRNA could be methylated enzymatically². Shershneva et al.³, however have shown that fragments are not methylated until recombined. Studies in our laboratory have demonstrated that certain fragments from a mixture of E. coli⁴ tRNAs can serve as substrate for rat liver tRNA methylases. These fragments are believed to have an average S value of 0.64 and therefore would be about ten nucleotides long. Using ultraviolet-induced alterations, we have investigated further the importance of the molecular shape of tRNA as it affects its recognition by tRNA methylases.