IDENTIFICATION AND MOLECULAR CHARACTERIZATION OF A YEAST MYOSIN-I

The family of myosin motors is comprised of numerous classes distribut ed among a diverse set of organisms and cell types. We have identified an unconventional myosin gene (MYO3) in the yeast Saccharomyces cerev isiae and show that it is member of a subclass of unconventional myosi n proteins originally found only in the amoeboid organisms Dictyosteli um and Acanthamoeba. Identification of this protein in these genetical ly and morphologically divergent organisms suggests that it will be ub iquitous in eukaryotes and that it has a role in the basic functions o f the eukaryotic cell. We have constructed a strain of yeast missing 9 9% of the MYO3 coding sequence. This mutation has no observable phenot ypic effect, placing MYO3 into a growing class of yeast genes which ar e dispensable under laboratory conditions, perhaps due to genetic redu ndancy. Alignment of MYO3 with other unconventional myosins shows that it shares with a subset of them a previously unrecognized region of h omology in the tail; this region falls within a domain identified as i mportant for mediating nonspecific electrostatic interactions with mem branes. The existence of this region suggests that it may be involved in mediating specific protein-protein interactions, possibly helping t o localize this myosin to specific membranes or membrane regions. In a ddition, we show that ''classic'' myosin I proteins share a region of hyper-proline-richness 10 amino acids before the SH3 domain. Proline-r ich regions have recently been implicated as SH3 binding sites, which suggests that this region might be involved with regulating or in othe r ways interacting with SH3 domains. (C) 1995 Wiley-Liss, Inc.