Specifically methylates the guanosine in position 748 of 23S rRNA. Confers resistance to the macrolide antibiotic tylosine. guanosine(748) in 23S rRNA + S-adenosyl-L-methionine = H(+) + N(1)-methylguanosine(748) in 23S rRNA + S-adenosyl-L-homocysteine Belongs to the methyltransferase superfamily. RlmA family.