Organization and expression of Drosophila tropomyosin genes

Abstract

A genomic clone containing two tropomyosin-coding sequences has been isolated from a library of Drosophila melanogaster DNA and identified by a positive hybridization selection and an in vitro translation procedure. In vitro translation yielded two products that comigrated with chicken and Drosophila tropomyosins in sodium dodecyl sulfate/polyacrylamide gels and underwent the mobility shift characteristic of vertebrate tropomyosins in sodium dodecyl sulfate/urea/polyacrylamide gels. The Drosophila polypeptides also shared several proteolytic fragments with chicken tropomyosins. The cloned DNA hybridized to a single site in region 88F 2–5 on the right arm of chromosome 3 of polytene chromosomes and to the set of restriction fragments in genomic DNA predicted from the cloned sequences, indicating that similar tropomyosin-coding sequences are not located at other sites in the genome. The 18 × 10 3 base-pair cloned segment contains three regions complementary to Drosophila embryo RNA separated by non-coding sequences. Two of these coding regions encode tropomyosin I and tropomyosin II; no protein product has been identified for the third coding region. The expression of the two tropomyosin genes is developmentally regulated during embryo development and in primary myogenic cultures, with abundant transcripts occurring at the onset of muscle cell fusion. The third coding region is homologous to abundant RNA transcripts found in earlier stages of embryo development, in primary myogenic cultures and in the Drosophila Kc cultured cell line.