Substitution of flight muscle-specific actin by human beta-cytoplasmic actin in the indirect flight muscle of Drosophila

The human beta-cytoplasmic actin differs by only 15 amino acids from Act88F actin which is the only actin expressed in the indirect flight muscle (IFM ) of Drosophila melanogaster, To test the structural and functional signifi cance of this difference, we ectopically expressed beta-cytoplasmic actin i n the IFM of Drosophila that lack endogenous Act88F, When expression of the heterologous actin was regulated by similar to 1.5 kb of the 5' promoter r egion of the Act88F gene, little beta-cytoplasmic actin accumulated in the IFM of the flightless transformants, Including Act88F-specific 5' and 3' un translated regions (UTRs) yielded transformants that expressed wild-type am ounts of beta-cytcoplasmic actin. Despite the assembly of P-cytoplasmic act in containing thin filaments to which endogenous myosin crossbridges attach ed, sarcomere organization was deficient, leaving the transformants flightl ess, Rather than affecting primarily actin-myosin interactions, our finding s suggest that the beta-cytoplasmic actin isoform is not competent to inter act with other actin-binding proteins in the IFM that are involved in the o rganization of functional myofibrils.