Figure 5.

Comparison of transverse sections from IFMs of wild-type and transformed flies. (A) In the wild-type IFM, myofibrils are round, uniform in diameter, and well ordered. They form hexagonal arrays of one thick myosin filament surrounded by six thin actin filaments. As marked by the black arrowheads, a thick filament is occasionally missing in an otherwise undisturbed filament lattice. (B) In transverse sections of C-terminally tagged transformants, there are no myofibrils assembled. As in cross-sections of the KM88 null mutant, thick filaments appear to be more or less randomly distributed and thin filaments are not evident. (C and D) Ordered myofibrillar structures are present in N-terminally tagged transformants. However, subtle effects of the tag on the structure are revealed. (D) In transformants expressing N-terminally 11-mer–tagged Act88F, the edges of the myofibrils appear frayed (black arrow). Occasionally, disturbances are detected in the hexagonal lattice of thick and thin filaments (white arrows). The inset reveals one of these disturbances at a twofold higher magnification. (C) On average, the myofibrils of transformants with an N-terminal 6xHis tag appear to have a slightly smaller (∼10%) diameter than myofibrils of wild-type IFM. Bar, 500 nm.