Abstract
Recent studies have revealed unconventional myosin V to be an important actin-based molecular motor involved in vesicular movement. In this paper we report the molecular characterization of the Drosophila myosin V, identified by reverse genetics. The gene encodes a 1792-residue, 207 kDa heavy chain polypeptide which possesses a typical head or motor domain of 771 residues, a region of six IQ motifs (139 residues) which serve as potential calmodulin/light chain binding sites at the head/tail junction, and a tail domain of 882 residues containing sequences of putative alpha-helical coiled-coils required for dimerization of the molecule and sequences of non-helical structure at the C-terminal end. Based on Southern blot analyses and chromosomal localization, evidence is presented for a single Drosophila myosin V gene. RNA analyses revealed a doublet of transcripts of about 6 kb, expressed throughout the lifetime of a fly but particularly abundant in the early stages of embryonic development (maternally contributed), in the ectodermic tissue of the hindgut starting at stage 16, and in the adult head. These results suggest that myosin V may be involved in processes required in a variety of cell types in Drosophila. We have also mapped the Drosophila myosin V locus to chromosome 2 at the position 43C-D, and we are currently searching for known mutations in this region. Finally, phylogenetic analysis of the head domain reveals that Drosophila myosin V is more closely related to mammalian myosin Va and Vb than to other invertebrate class-V myosins; nevertheless, it is not significantly more related to myosin Va than to myosin Vb. While vertebrates would need two different myosin V isoforms to accomplish specific functions, we speculate that Drosophila myosin V might provide the equivalent functions by itself.
