Fig. 4. The position of myofilin in Drosophila muscles. (A) Thin, slightly oblique cryosection of Drosophila IFM labelled with anti-myofilin and Protein A-gold. The fibre is slightly stretched to increase the length of the I-band. Gold particles are in diagonal lines across the sarcomere; this results from exposure of epitopes by the knife cutting through the regular thick filament lattice (Ferguson et al., 1994). The positions of H-zone (H), A-band (A), I-band (I), Z-band (Z) are shown. Horizontal lines mark the extent of the A-band. Beneath the micrograph is a histogram showing the distribution of gold particles and the corresponding density profile across the sarcomere. Gold particles extend to the edges of the A-band and H-zone. (B) Cryosection of non-flight muscle labelled with anti-myofilin and Protein A-gold. In this case the myofibrils are narrower and the sarcomeres longer, so that the H-zones are not visible in this micrograph. Labelling is less regular, but again extends to the end of the A-band. Bar, 200 nm.