Contribution to clusters. Contribution of the different kingdoms to the complete sequence pool analyzed (A) and to SMC, myosin and kinesin clusters (B). Y-axis, number of sequences; X-axis, cluster IDs. Examples for characteristic protein families represented in clusters are as follows: clusters 99, 172, 717, SMC 1–4; cluster 165, SMC 5–6; clusters 39, 1220, type II myosins; cluster 125, type X myosins; cluster 1223, non-muscle myosins; clusters 1, 272, KIFCs; clusters 157, 220, PAKRPs; cluster 244, NACK, MKRPs. Proteins may qualify for two or more overlapping cluster, e.g. resulting in prokaryotic SMCs clustering with different types of diverged eukaryotic SMC proteins.