L-aspartate(89)-[ribosomal protein uS12]-hydrogen + (sulfur carrier)-SH + AH2 + 2 S-adenosyl-L-methionine = 3-methylsulfanyl-L-aspartate(89)-[ribosomal protein uS12]-hydrogen + (sulfur carrier)-H + 5'-deoxyadenosine + L-methionine + A + S-adenosyl-L-homocysteine + 2 H(+) — reaction