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Biosynthesis of tropomyosin and troponin during development of the chicken skeletal muscle.

The level of functional mRNA coding for myofibrillar proteins was studied during development of the chicken skeletal muscle. RNA isolated from the developing chicken muscle directed protein synthesis in a wheat germ cell-free system. By means of polyacrylamide gel electrophoresis and immunological analysis, tropomyosin subunits and troponin components were identified among the cell-free translation products. The mRNA activities for alpha- and beta-subunit of tropomyosin were prominent in the embryonic breast muscle as well as in the embryonic leg muscle. At the early post-embryonic stage, the mRNA activity for beta-subunit disappeared from the breast muscle, while those for alpha- and beta-subunit were detectable in the leg muscle. Troponin-C and troponin-I synthesized in vitro in response to the muscle RNA formed a binary complex in the presence of calcium ion. Despite the observed difference in molecular weight between troponin-Ts in the breast and leg muscle, RNA preparations from the two muscles encoded identical troponin-Ts whose molecular weights were indistinguishable from that of troponin-T present in the breast muscle of adult chicken. It is suggested from these results that the biosynthesis of tropomyosin is regulated at the pre-translational level during the development of the chicken skeletal muscle, whereas post-translational (or co-translational) events may produce the tissue-specific form of troponin-T.