The genetic analysis of MYO1, a gene encoding a type II myosin in Saccharomyces cerevisiae.

The genetic analysis of MYO1, a gene encoding a type II myosin in Saccharomyces cerevisiae. By F.P. Sweeney, B.Sc., M.Sc. Department of Genetics, University of Leicester, U.K. The MYO1 gene (5.55 kb) from Saccharomyces cerevisiae has been completely sequenced. The predicted polypeptide has a molecular mass of 213 kDa and is shown to be a type II myosin. The N-terminal domain displays high sequence similarity to those of other myosins, whereas the C-terminal region contains the seven and twenty eight residue repeating motifs characteristic of type II myosins. Six proline residues are located within the tail region, at approximately two thirds from the start of the tail. Gene disruption has been used to investigate the biological function of a 4kDa C-terminal fragment of the yeast myosin. Disruption of MYO1 by the URA3 gene gave rise to cells defective in both cytokinesis and nuclear migration, similar to the null phenotype. When the MYO1 gene was disrupted at the same location with the TRP1 gene, the resulting cells displayed no defect in either cytokinesis or nuclear migration. It is predicted that 16 residues in the TRP1 sequence form a fusion protein with the myosin which restores its activity. Over-expression of the MYO1 gene product from a galactose inducible promoter is shown to be lethal. The purified yeast myosin, visualised by electron microscopy, consists of two globular head regions attached to an extended tail, similar to mammalian type II myosins.