MULTIPLE ISOELECTRIC VARIANTS OF FLIGHTIN IN DROSOPHILA STRETCH-ACTIVATED MUSCLES ARE GENERATED BY TEMPORALLY REGULATED PHOSPHORYLATIONS

Drosophila stretch-activated flight muscles contain flightin, a novel myofibrillar protein that interacts with myosin filaments. We have ide ntified eleven flightin isoelectric variants that can be subdivided in to phosphorylated and non-phosphorylated subclasses. Flight muscles of late pupal stage P15, at which time myofibrillogenesis has been compl eted but the muscle has yet to be used, contain primarily non-phosphor ylated variants. A dramatic increase in flightin phosphorylation occur s subsequent to eclosion. As the young adult matures, increasingly pho sphorylated variants are generated following a precise ontogenetic pro gression. Adults 5-6 h old and older contain the entire set of flighti n isoelectric variants. All nine phosphovariants remain metabolically active throughout adult life as evidenced by their ability to incorpor ate radioactive phosphate in older adults. Our results suggest the pos sibility that all nine phosphorylated variants originate from a single precursor by sequential phosphorylation. Phosphorylation of flightin may thus serve both structural and regulatory functional roles.