Stress-induced modification of tRNA generates 5-methylcytidine in the variable loop.

There has been recent interest in trying to understand the connection between transfer RNA (tRNA) posttranscriptional modifications and changes in-cellular environmental conditions. Here, we report on the identification of the modified nucleoside 5-methylcytidine (mC) in tRNAs. This modification was determined to be present at position 49 of tRNA Tyr-QUA-II. Moreover, mC levels in this tRNA are significantly elevated under high reactive oxygen specieis (ROS) conditions in cells. We identified the known ribosomal RNA methyltransferase rsmF as the enzyme responsible for mC synthesis in tRNA and enzyme transcript levels are responsive to elevated levels of ROS in the cell. We further find that changes in mC levels in this tRNA are not specific to Fenton-like reaction conditions elevating ROS, but heat shock can also induce increased modification of tRNA Tyr-QUA-II. Altogether, this work illustrates how cells adapt to changing environmental conditions through variations in tRNA modification profiles.