A number of enzymes responsible for the dimethylation of adenosines in ribosomal RNAs (EC 2.1.1.48) have been found [1,2] to be evolutionary related. These enzymes are:

• Bacterial 16S rRNA dimethylase (gene ksgA), which acts in the biogenesis of ribosomes by catalyzing the dimethylation of two adjacent adenosines in the loop of a conserved hairpin near the 3'-end of 16S rRNA. Inactivation of ksgA leads to resistance to the aminoglycoside antibiotic kasugamycin.
• Yeast 18S rRNA dimethylase (gene DIM1), which is functionally similar to ksgA and that dimethylates twin adenosines in the 3'-end of 18S rRNA.
• Bacterial 'erm' methylases. These enzymes confer resistance to macrolide- lincosamide-streptogramin B (MLS) antibiotics - such as erythromycin - by dimethylating the adenine residue at position 2058 of 23S rRNA thus resulting in a reduced affinity between ribosomes and the MLS antibiotics.
• Caenorhabditis elegans hypothetical protein EO2H1.1.

The best conserved region in these enzymes is located in the N-terminal section and corresponds to a region that is probably involved in S-adenosyl methionine (SAM) binding.