title: Two Drosophila melanogaster tropomyosin genes: structural and functional aspects.
abstract: We compared the structure and function of the two Drosophila melanogaster tropomyosin genes. The most striking structural aspect was their size disparity. Codons 1 through 257 of gene 2 occupied 833 nucleotides and contained only one intron, whereas the corresponding region of gene 1 occupied 17.5 kilobases and was interrupted by eight introns. The intron-exon arrangement of gene 1 reflected evolutionary expansion of tropomyosin via 42- and 49-residue duplications, which are probably actin-binding domains. Functionally, gene 1 was considerably more complex than gene 2; it was active in both muscle and nonmuscle cell lineages, had at least five variable exons, and specified a minimum of five developmentally regulated isoforms. Two of these isoforms, which accumulated only in flight muscles, were unprecedented fusion proteins in which the tropomyosin sequence was joined to a carboxy-terminal proline-rich domain.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D003001:Cloning, Molecular; D004247:DNA; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development; D005786:Gene Expression Regulation; D005796:Genes; D007438:Introns; D009132:Muscles / Q000502:physiology; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics; D014018:Tissue Distribution; D014335:Tropomyosin / Q000235:genetics*
chemical_list: D029721:Drosophila Proteins; D012333:RNA, Messenger; C490776:Tm1 protein, Drosophila; D014335:Tropomyosin; D004247:DNA