Isolation and chracterization of m5U-methyltransferase from Escherichia coli

The tRNA-modifying enzyme, S-adenosylmethionine: tRNA (uridine-5)-methyltransferase, has been purified essentially to homogeneity from an Escherichia coli strain containing an elevated level of this enzyme. A rapid, efficient method has been developed for the purification, consisting of polyethyleneimine precipitation to remove nucleic acids, followed by phosphocellulose and Blue Sepharose affinity chromatography. The enzyme is a single polypeptide chain of molecular weight 42,000. It has a pH optimum of 8.4, a Km of 12.5 microM for S-adenyosyl-L-methionine, and a Km of 1.1 microM for wheat germ tRNAGly1. The ability of the enzyme to methylate a variety of tRNA substrates including prokaryotic, eukaryotic, mitochondrial, and chloroplastic tRNAs has been characterized.