FLIGHTIN, A NOVEL MYOFIBRILLAR PROTEIN OF DROSOPHILA STRETCH-ACTIVATED MUSCLES

The indirect flight muscles of Drosophila are adapted for rapid oscill atory movements which depend on properties of the contractile apparatu s itself. Flight muscles are stretch activated and the frequency of co ntraction in these muscles is independent of the rate of nerve impulse s. Little is known about the molecular basis of these adaptations. We now report a novel protein that is found only in flight muscles and ha s, therefore, been named flightin. Although we detect only one gene (i n polytene region 76D) for flightin, this protein has several isoforms (relative gel mobilities, 27-30 kD, pIs, 4.6-6.0) These isoforms appe ar to be created by posttranslational modifications. A subset of these isoforms is absent in newly emerged adults but appears when the adult develops the ability to fly. In intact muscles flightin is associated with the A band of the sarcomere, where evidence suggests it interact s with the myosin filaments. Computer database searches do not reveal extensive similarity to any known protein. However, the NH2-terminal 1 2 residues show similarity to the NH2-terminal sequence of actin, a re gion that interacts with myosin. These features suggest a role for fli ghtin in the regulation of contraction, possibly by modulating actin- myosin interaction.