a-c, Models of the cryo-EM structures in the indicated cofactor binding states, in cartoon representation. METTL1, WDR4, tRNA and SAM/SAH are colored blue, green, gold, and magenta, respectively. d, Superimposition of the apo and SAH-bound cryo-EM structures of METTL1-WDR4-tRNA, aligning by WDR4. METTL1 moves closer to tRNA in the presence of SAH (black dashed arrow). e, Zoomed-in view of (d) showing the tRNA and the catalytic loop protruding toward the tRNA (black dashed arrow).