TROPONIN-T IS A CALCIUM-BINDING PROTEIN IN INSECT MUSCLE - IN-VIVO PHOSPHORYLATION, MUSCLE-SPECIFIC ISOFORMS AND DEVELOPMENTAL PROFILE IN DROSOPHILA-MELANOGASTER

Two sets of muscle polypeptides showing calcium-binding capacity and i ntense labelling in vivo with P-32 were purified and characterized fro m Drosophila melanogaster adult extracts. The polypeptides exhibit cro ssed immunoreactivity and share similar biochemical properties such as those involved in purification. They have been identified as isoforms of troponin-T (TnT) by sequence analysis of a cDNA clone isolated fro m an embryonic library. The two sets of TnT polypeptides correspond to the fibrillar and non-fibrillar muscle isoforms, respectively. The no n-fibrillar muscle isoforms separate into two bands which are differen tially expressed during development. Analysis of TnT isoforms in bee t horaces indicates that the expression of the fibrillar muscle isoform correlates with the acquisition of functional flight capability. In vi vo labelling experiments reveal that the two TnT sets are readily phos phorylated. The Drosophila TnTs show calcium-binding properties by thr ee different types of assays. Our results suggest that this property c ould be specific to insect TnTs and may be related to the long, extrem ely acidic polyglutamic carboxy-terminus present in these polypeptides , which does not occur in non-arthropod TnTs. (C) Chapman & Hall Ltd.