Troponin proteins associate with tropomyosin and regulate the calcium sensitivity of the myofibril contractile apparatus of striated muscles. Each troponin-tropomyosin complex contains 1 molecule from each of the 3 troponins: T, C, and I. The troponin I (TNI) subfamily contains three genes: TNI-skeletal-fast-twitch, TNI-skeletal-slow-twitch, and TNI-cardiac. TNNI1 prevents muscle contraction by inhibiting calcium-mediated conformational changes in actin-myosin complexes.