Evolution of the first myosins. The first myosin, called ur-myosin, is expected to consist only of the myosin motor domain. By domain fusion it generated the IQ motif either directly carboxy-terminal to the motor domain (2), or after a gene duplication event (1). After a further gene duplication event, this myosin developed to the class-I myosins as well as the ancestor of most of the other myosin classes after fusion with an SH3 domain (which developed into the amino-terminal SH3-like domain).
Odronitz and Kollmar Genome Biology 2007 8:R196 doi:10.1186/gb-2007-8-9-r196