C-methyltransferase that acts together with NovW to catalyze the formation of dTDP-4-keto-6-deoxy-5-C-methyl-L-lyxo-hexose from dTDP-4-keto-6-deoxy-D-glucose in the novobiocin biosynthesis pathway, an aminocoumarin family antibiotic that targets bacterial DNA gyrases. Antibiotic biosynthesis; novobiocin biosynthesis. It is unclear whether NovU acts before or after 3-epimerase NovW in the novobiocin biosynthesis pathway. Belongs to the methyltransferase superfamily.