Is nebulin truly a component of the thin filament

Nebulin is a protein coextensive with thin filament in skeletal muscle. Several evidences seem to indicate that nebulin may be a component of the thin filament. We prepared thin filaments from rabbit and beef skeletal muscle by extraction of myofibrils at high and at low ionic strength. At the end of the purification procedure, nebulin was always found in the fraction containing the thick filaments and was absent from the fraction containing the thin filaments. We propose therefore that, even if nebulin binds to thin filaments, the binding is very week