Sequence motifs and amino acid content-based MTase clustering. A similarity network approach to distinguish the sequence relationships among the RNA MTases. Edges are represented by Similarity Index scores (see Amino acid profiles at Methods) and Nodes are denoted by a function assigned to each MTase as follows: 16S rRNA MTases (blue), 23S RNA MTases (green), tRNA MTases (red), ribosome protein MTase (orange), cofactor/vitamin biosynthesis MTase (gray), unknown function (black). The numbers located inside the nodes in B and D panels indicate connectivity (number of interactions). The A and B panels show the Similarity Network for E. coli K12, whereas the C and D panels indicate that for B. subtilis 168. E – Heatmap built from information on the relative amino acid distributions among all the MTase families detected in the Similarity Networks. *Refers to the N-terminal domain of the bi-functional MnmC enzyme.