A nonsense mutation within the act88f actin gene disrupts myofibril formation in Drosophila indirect flight muscles

Abstract We have investigated the molecular basis of muscle abnormalities in the flightless Drosophila mutant Ifm(3)7. This EMS-induced, semi-dominant allele was isolated by Mogami and Hotta 1981 and was shown to disrupt the organization of myofibrils in indirect flight muscles. Here we demonstrate that Ifm(3)7 contains a nonsense mutation within codon 355 of the act88F actin gene. A single G>A transition converts a tryptophan (TGG) codon to an opal (TGA) terminator, thus deleting the carboxy-terminal 20 amino acids of an actin isoform that accumulates only in thoracic flight muscles. The truncated actin polypeptide is stable, and retains antigenicity to at least two anti-Drosophila actin monoclonal antibodies. We suggest that abnormalities in Ifm(3)7 flight muscles result from incorporation of the mutant actin isoform into assembling myofibrils.