Catalysis of the reaction: 5-aminomethyl-2-thiouridine34 in tRNA + S-adenosyl-L-methionine = 5-methylaminomethyl-2-thiouridine34 in tRNA + H+ + S-adenosyl-L-homocysteine. This enzyme specifically adds the terminal methyl group of 5--2-thiouridylate.
tRNA 5-methylaminomethyl-2-thiouridylate 5\'-methyltransferase activity