DROSOPHILA PARAMYOSIN MINIPARAMYOSIN GENE-PRODUCTS SHOW A LARGE DIVERSITY IN QUANTITY, LOCALIZATION, AND ISOFORM PATTERN - A POSSIBLE ROLE IN MUSCLE MATURATION AND FUNCTION

The Drosophila paramyosin/miniparamyosin gene expresses two products o f different molecular weight transcriptionally regulated from two diff erent promoters. Distinct muscle types also have different relative am ounts of myosin, paramyosin, and miniparamyosin, reflecting difference s in the organization of their thick filaments. Immunofluorescence and EM data indicate that miniparamyosin is mainly located in the M line and at both ends of the thick filaments in Drosophila indirect flight muscles, while paramyosin is present all along the thick filaments. In the tergal depressor of the trochanter muscle, both proteins are dist ributed all along the A band. In contrast, in the waterbug, Lethocerus , both paramyosin and miniparamyosin are distributed along the length of the indirect flight and leg muscle thick filaments. Two-dimensional and one-dimensional Western blot analyses have revealed that minipara myosin has several isoforms, focusing over a very wide pH range, all o f which are phosphorylated in vivo, The changes in isoform patterns of miniparamyosin and paramyosin indicate a direct or indirect involveme nt of these proteins in muscle function and flight. This wide spectrum of potential regulatory characteristics underlines the key importance of paramyosin/miniparamyosin and its complex isoform pattern in the o rganization of the invertebrate thick filament.