The myosins are a superfamily of protein motors. Analysis of their sequences in a wide range of organisms reveals an unexpected variety of domains, and provides insights into the nature of the earliest eukaryotes. Motor proteins use chemical energy, for example from ATP, to generate unidirectional movement along a filamentous track. How a group of proteins acquired and then varied this property to generate a range of movements as evolution proceeded is a fascinating problem in biology. Answers are within reach because of the availability of genome sequences from a diverse cadre of organisms representing various evolutionary groups. This allows in-depth compaiative analyses of the sequences of protein families and the incorporation of these data intomodels of evolution. Richards and Cavalier-Smith (page 1113 of this issue) have performed a comprehensive analysis of the rnyosin superfamily of motor proteins across a wide sample of eukaryotes (organisms whose cells have nuclei, including plants and animals). The results provide insights into how myosins evolved and into the nature of the earliest common ancestor — the cenancestor — of eukaryotic cells.
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