Reannealing of beta-actinin-severed actin filaments by troponin and tropomyosin.

During a survey of actin pointed end-capping protein in salt extracts of rabbit skeletal muscle, it was found that native tropomyosin (troponin-tropomyosin complex) inhibited the seed activity of beta-actinin-capped actin filaments for actin polymerization. It turned out that beta-actinin-capped actin fragments reannealed to form long filaments resulting in the decrease in seed numbers in the presence of troponin and tropomyosin. It appears that the reannealing of actin filaments was due to release of beta-actinin from the actin filaments by troponin and tropomyosin. Either troponin or tropomyosin alone was not effective at all. Addition of an excess amount of beta-actinin did not prevent the reannealing of beta-actinin-capped actin filaments in the presence of troponin and tropomyosin.