23S rRNA (guanine<sup>2535</sup>-N<sup>1</sup>)-methyltransferase (, AviRa) is an enzyme with systematic name S-adenosyl-L-methionine:23S rRNA (guanine<sup>253</sup>5-N<sup>1</sup>)-methyltransferase. This enzyme catalyses the following chemical reaction
This is one of the methyltransferases from Streptomyces viridochromogenes . Streptomyces viridochromogenes produces the antibiotic avilamycin A which binds to the 50S ribosomal subunit to inhibit protein synthesis.