Involved in the biosynthesis of nocamycin I and nocamycin II (PubMed:28818448). Catalyzes the methylation of nocamycin E to yield nocamycin I (PubMed:28818448). nocamycin E + S-adenosyl-L-methionine = nocamycin I + S-adenosyl-L-homocysteine Antibiotic biosynthesis. Mutant loses the capability to produce nocamycin I and nocamycin II. Mutant produces a new nocamycin intermediate, 21-demethyl-nocamycin I, which was designated as nocamycin E. Belongs to the methyltransferase superfamily. Extended N-terminus.