O ver 60 y have elapsed since John Pringle (1) described a remarkable property of insect flight muscles: If you stretch them, after short a delay, they exert more force. This explains how insects beat their wings. The flight muscles are organized in antagonistic pairs coupled to the wing. The system is a free-running oscillator: Each time one muscle contracts, it stretches the opposing muscle, ...

Antitropomyosin and anti-alpha-actinin monoclonal antibodies have been used to isolate two classes of microfilaments, i.e., tropomyosin-enriched and alpha-actinin-enriched microfilaments, respectively, from cultured chicken embryo fibroblasts. Electron microscopic studies of the isolated tropomyosin-enriched microfilaments showed periodic localization of tropomyosin along the microfilaments, wi...

Phenotypically altered C2 myoblast cells, generated by the stable transfection of human nonmuscle actin genes (Schevzov, G., C. Lloyd, and P. Gunning. 1992. J. Cell Biol. 117:775-786), exhibit a differential pattern of tropomyosin cellular organization and isoform gene expression. The beta-actin transfectants displaying a threefold increase in the cell surface area, showed no significant change...

We isolated a cDNA clone from the tumorigenic human fibroblast cell line HuT-14 that contains the entire protein coding region of tropomyosin isoform 3 (Tm3) and 781 base pairs of 5'- and 3'-untranslated sequences. Tm3, despite its apparent smaller molecular weight than Tm1 in two-dimensional gels, has the same peptide length as Tm1 (284 amino acids) and shares 83% homology with Tm1. Tm3 cDNA h...

We expressed the following fragments of chicken gizzard caldesmon in the pMW 172/BL21 (DE3) system at 0.4-2.2 mg of pure protein/liter of culture: full-length smooth muscle caldesmon (CDh) (amino acids 1-756), nonmuscle caldesmon (CDl), amino acids 1-128 (N128), 1-578 (N578), 230-419, 606-756 (606C), and 658-756 (658C). CDh bound tropomyosin with a Kd of 1.5 microM; N578, 230-419, and 606C boun...

Ovulation in the nematode Caenorhabditis elegans is coordinated by interactions between the somatic gonad and germ cells. Myoepithelial sheath cells of the proximal ovary are smooth muscle-like cells, but the regulatory mechanism of their contraction is unknown. We show that contraction of the ovarian muscle requires tropomyosin and troponin, which are generally major actin-linked regulators of...

Muscle contraction is regulated by troponin-tropomyosin, which blocks and unblocks myosin binding sites on actin. To elucidate this regulatory mechanism, the three-dimensional organization of troponin and tropomyosin on the thin filament must be determined. Although tropomyosin is well defined in electron microscopy helical reconstructions of thin filaments, troponin density is mostly lost. Her...

We have investigated the cumulative effects of three smooth-muscle actin-binding proteins, gelsolin, caldesmon and tropomyosin, on actin activation of myosin Mg(2+)-ATPase activity under low-ionic-strength conditions. A combination of tropomyosin (at a stoicheiometric ratio to actin) and gelsolin (at a molar ratio to actin of up to 1:100) showed essentially additive stimulatory effects that wer...

PURPOSE To determine the role of the actin cytoskeleton regulatory proteins tropomyosin and tropomodulin (Tmod) in the reorganization of the actin cytoskeleton during lens epithelial cell differentiation. METHODS Primary cultures of chick lens epithelial cells were allowed to differentiate in vitro to form lentoid bodies. Localization of F-actin, Tmod, and tropomyosin were determined by immun...

Precipitation at pH 5.6 is found to improve the rabbit muscle troponin preparation. Further purification of troponin is achieved by treating troponin preparations with 0.1 M dithiothreitol, followed by the removal of contaminating tropomyosin by gel filtration. This is possible because through these purification procedures the molecular weight of tropomyosin as estimated by gel filtration remai...