A Myosin I Isoform in the Nucleus

Abstract
A nuclear isoform of myosin I β that contains a unique 16–amino acid amino-terminal extension has been identified. An affinity-purified antibody to the 16–amino acid peptide demonstrated nuclear staining. Confocal and electron microscopy revealed that nuclear myosin I β colocalized with RNA polymerase II in an α-amanitin– and actinomycin D–sensitive manner. The antibody coimmunoprecipitated RNA polymerase II and blocked in vitro RNA synthesis. This isoform of myosin I β appears to be in a complex with RNA polymerase II and may affect transcription.