MOLECULAR CHARACTERIZATION OF MYOSIN-V FROM DROSOPHILA-MELANOGASTER

Recent studies have revealed unconventional myosin V to be an importan t actin-based molecular motor involved in vesicular movement. In this paper we report the molecular characterization of the Drosophila myosi n V, identified by reverse genetics. The gene encodes a 1792-residue, 207 kDa heavy chain polypeptide which possesses a typical head or moto r domain of 771 residues, a region of six IQ motifs (139 residues) whi ch serve as potential calmodulin/light chain binding sites at the head / tail junction, and a tail domain of 882 residues containing sequence s 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, evi dence 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 o f embryonic development (maternally contributed), in the ectodermic ti ssue of the hindgut starting at stage 16, and in the adult head. These results suggest that myosin V may be involved in processes required i n a variety of cell types in Drosophila. We have also mapped the Droso phila myosin V locus to chromosome 2 at the position 43C-D, and we are currently searching for known mutations in this region. Finally, phyl ogenetic analysis of the head domain reveals that Drosophila myosin V is more closely related to mammalian myosin Va and Vb than to other in vertebrate 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 s peculate that Drosophila myosin V might provide the equivalent functio ns by itself. (C) Chapman & Hall Ltd.