S-adenosylmethionine-dependent methyltransferase activity precorrin-3B C17-methyltransferase activity https://github.com/geneontology/go-ontology/issues/30193 S-adenosyl-L-methionine:precorrin-3B C17-methyltransferase activity CobJ molecular_function EC:2.1.1.131 RHEA:12761 precorrin-3 methylase activity MetaCyc:2.1.1.131-RXN precorrin-3 methyltransferase activity Catalysis of the reaction: S-adenosyl-L-methionine + precorrin-3B = S-adenosyl-L-homocysteine + precorrin 4. GO:0030789