S-adenosyl-L-methionine-dependent methyltransferase that catalyzes the formation of 5-methyl-uridine in tRNAs and some mRNAs. Mainly catalyzes the methylation of uridine at position 54 (m5U54) in cytosolic tRNAs. Also able to mediate the formation of 5-methyl-uridine in some mRNAs. S-adenosyl-L-methionine + uridine(54) in tRNA = 5-methyluridine(54) in tRNA + H(+) + S-adenosyl-L-homocysteine a uridine in mRNA + S-adenosyl-L-methionine = a 5-methyluridine in mRNA + H(+) + S-adenosyl-L-homocysteine Widely expressed at low level. Expressed at higher level in proliferating cells. In a cell-cycle manner (PubMed:9224656, PubMed:9417108). Transcription is activated at the G1/S transition of the cell cycle and peaks in S phase, while being repressed in quiescent tissues and growth-arrested cells (PubMed:9417108). Htf9a (RanBP1) and Trmt2a are transcribed with opposite polarity from complementary DNA strands from a shared bidirectional TATA-less promoter. Belongs to the class I-like SAM-binding methyltransferase superfamily. RNA M5U methyltransferase family.