N2-Guanine specific transfer RNA methyltransferase I from rat liver and leukemic rat spleen
Open Access
- 1 January 1974
- journal article
- Published by Oxford University Press (OUP) in Nucleic Acids Research
- Vol. 1 (11), 1455-1478
- https://doi.org/10.1093/nar/1.11.1455
Abstract
An enzyme was purified from rat liver and leukemic rat spleen wnich methylates guanosine residues in tRNA to li2-methylguanosine. By sequence analysis of bulk E. coli tRNA methylated with crude extracts it was shown that the enzyme is responsible for about 50% of total m2G formed in vitro. The extent of methylation of a number of homogenous tRNA species was measured using the purified enzyme from both sources. Among tested E. coli tRNAs only tRNAArg, tRNAPhe, and tRNAVal yielded significantly more m2G than the bulk tRNA. The Km for tRNAArg in the methylation reaction with enzymes from either tissue was 7.8 × 10-7 M as compared to the value 1 × 10-5 M obtained for the bulk tRNA. In a pancreatic RNase digest of bulk tRNA as well as of pure tRNAArg, tRNAPhe, and tRNAVal, A-m2G-Cp was found to be the only sequence methylated. Thus, the mammalian methyl-transferase specifically recognizes the guanylate residue at position 10 from the 5′-end contained in a sequence (s4)U-A-G-Cp. Furthermore, there is no change between the enzyme from normal liver and leukemic spleen in the affinity for tRNA, the methylating capacity, and tRNA site and sequence recognition specificity.Keywords
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