RlmB is a SPOUT-type of methyltransferase catalyzing formation of Gm at the conserved position 2251 in the peptidyltransferase domain V of large subunit rRNA (hairpin 80, also named P-loop). The ortholog SPOUT enzyme in S. cerevisiae is Mrm1 (formerly Pet56) catalyzing Gm at equivalent position 2270 (S. cerevisiae numbering) in large subunit mitochondrial rRNA. In cytoplasmic rRNA, the same conserved Gm is catalyzed at position 2619 (S. cerevisiae numbering) by C/D box RNP, guided by snR67. AdoMet is the donor of methyl group. The N-terminal domain of E. coli RlmB is similar to those in ribosomal proteins L7 and L30.