Tropomyosin is semi-modular protein, comprised of an elongated coiled coil that stretches along the thin filament and weakly interacts with multiple actin monomers. Despite the weakness of these interactions, they accomplish potent regulatory effects. In muscle thin filaments, tropomyosin increases myosin S1-actin binding affinity ∼4-fold (either + or - ADP.) Deletional studies suggest (but do not prove) that this average effect of the entirety of muscle tropomyosin varies among the seven quasi-repeating regions of the molecule. To test this hypothesis, different quasi-repeats of alpha-striated muscle tropomyosin were inserted into Saccharomyces cerevisiae tropomyosin isoform TPM1, swapping out a region of the yeast isoform potentially well suited for such maneuvers. Importantly, TPM1 does not greatly affect myosin-actin binding. Also, its residues 70-107 span one actin, are an internal repeat region, and have heptad phase staggered at each end. A series of chimeric tropomyosins was generated by replacing these 38 residues of TPM1 with heptad phase- and length-corresponding sections of muscle tropomyosin. Five of 7 such chimeric tropomyosins bound poorly to actin and to actin-S1, despite coiled-coil folding. Chimeras containing muscle tropomyosin residues 74-111 and 228-265 bound tightly to actin, and thus could be studied for functional effects of the residue substitutions. When myosin S1 was added, it increased chimera 74-111 binding to actin and decreased chimera 228-265 association with actin. None of the chimeric tropomyosins altered the actin-activated ATPase rate of skeletal muscle S1. Effects on S1-ADP binding to actin are under examination. The results support the concept that the effects of muscle tropomyosin on myosin-actin interactions are not homogeneous along the seven-actin spanning length of this regulatory protein.