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Abstract
A cDNA encoding skeletal fast troponin I (Tnlf) has been isolated and characterized from an adult rabbit fast skeletal muscle cDNAlibrary. This cDNA contains the entire coding region of 549 base pairs (bp), the 3' untranslated (UT) segment of 78 bp and the 5' UT segment of 74 bp. The 3' UT segment shows the predicted stem-loop structure characteristic of eukaryotic mRNAs. The cDNA-derived amino acid sequence is not identical to the chemically-derived and the recently reported cDNA-derived amino acid sequences for rabbit Tnlf, and thus enables to make the necessary corrections in the sequence information. The rabbit Tnlf is encoded by a single copy gene which is expressed in adult fast skeletal muscle in a tissue-specific manner. Comparative sequence analysis of the vertebrate Tnl isoforms and their cDNAs shows a high level of sequence conservation in the coding region among the Tnlf interspecies isoforms. The sequence similarity is markedly decreased among the fast, slow and cardiac intra-and inter-species isoforms. The C-terminal halves of Tnl isoforms including a segment believed to be involved in critical interactions with actin and troponin C (TnC) show high sequence conservation whereas the N-terminal halves show considerable difference in sequence and size. The significance of these results in relation to the biological function and evolution of members of the vertebrate Tnl multigene family is discussed.