N2-guanine specific transfer RNA methyltransferase II from rat liver

Abstract

N(2)-guanine methyltransferase II was purified from rat liver. This enzyme methylated bulk E. coli tRNA to an extent of 7.6 nmoles of methyl groups/mg tRNA. Oligonucleotide analysis showed that N(2)-methylated guanosines were present in the modified tRNA in two sequences, namely Y-m(2)G-Cp and Y-m(2) (2)G-Cp in the ratio 4:3. Two pure tRNA(Leu) species, and tRNA(Met) (f) from E. coli were methylated with the enzyme to extents of 17, 11, and 8 nmoles of methyl groups incorporated per mg tRNA, respectively. When the methylated tRNAs were analysed no m(2) (2)G was detected and the m(2)G occurred in the tRNAs specific for leucine in a Y-m(2)G-Cp sequence and in the tRNA(Met) (f) in a sequence Y-m(2)G-Up.It is concluded that the mammalian enzyme specifically recognizes the interstem unpaired guanylate residue between the dihydrouridine arm and the anticodon arm. The absence of any detectable m(2) (2)G methylation of individual tRNA species is discussed.