InterPro domain: IPR023165

KsgA is a universally conserved rRNA adenine dimethyltransferase that catalyses the transfer of a total of four methyl groups from S-adenosyl-l-methionine (S-AdoMet) to two adjacent adenosine bases in 16S rRNA. This enzyme and the resulting modified adenosine bases appear to be conserved in all species of eubacteria, eukaryotes, and archaebacteria, and in eukaryotic organelles. The KsgA enzymes are homologous to another family of RNA methyltransferases, the Erm enzymes, which methylate a single adenosine base in 23S rRNA [ 1 ].

This superfamily represents a rRNA adenine dimethylase-like domain present in these enzymes, which consists of four alpha-helices and one 3(10)-helix and forms a cleft with the N-terminal domain and is thought to stabilise it. Other studies have suggested that due to the positively charged surface patch, the C-terminal domain may be involved in recognition and binding of the ribosomal rRNA substrate, and mediates substrate specificity [ 2 , 3 ].

1. Crystal structure of KsgA, a universally conserved rRNA adenine dimethyltransferase in Escherichia coli. J. Mol. Biol. 339, 337-53
2. Structural rearrangements in the active site of the Thermus thermophilus 16S rRNA methyltransferase KsgA in a binary complex with 5'-methylthioadenosine. J. Mol. Biol. 388, 271-82
3. Structural basis for S-adenosylmethionine binding and methyltransferase activity by mitochondrial transcription factor B1. Nucleic Acids Res. 41, 7947-59