Heat shock gene activation by mutant actin is independent of myofibril degeneration in Drosophila muscle.

Artificially mutagenized Drosophila Act88F actin genes with triple and double mutations were expressed in the indirect flight muscles of transgenic flies. The triple mutant actin, GD245T (Gly-36----Glu, Glu-83----Asp, and Gly-245----Asp), induced heat shock protein (hsp) synthesis without affecting flight ability. On the other hand, the double mutation, GD245D (Gly-36----Glu and Glu-83----Asp), disrupted myofibrils but induced little hsp synthesis. These results demonstrate that myofibril degeneration is not the primary cause of the anomalous heat shock gene activation by mutant actins.