Complete Coding Sequences of CDNAs of Four Variants of Rabbit Skeletal Muscle Troponin T

Four variants of troponin T (TnT) cDNAs have been isolated and sequenced. These cDNAs have been derived from rabbit skeletal muscle, the most widely studied source of troponin, of a 11-day-old animal. One variant (TnT-1) contains the complete coding sequence, while in three variants the coding sequences are truncated at the 5' termini. The previously published amino acid sequence differs from the present cDNA-derived sequences at three locations. At least two, possibly all, of them are probably accounted for by errors in peptide sequencing. The present results are consistent with the two types of alternative splicing of TnT genes, both being first reported on the rat gene. (1) Highly variable sequences in the amino-terminal region are accounted for by the alternative splicing of exons 4-8 in an interchangeable but not mutually exclusive manner. (2) In the carboxyl-terminal region, the alternative splicing of two exons 17 (beta-type) or 16 (alpha-type) in mutually exclusive manner is consistent with the difference between all the four cDNAs, which express exon 17, and the previously published peptide sequence (derived from the adult muscle) in which exon 16 is present. This variation also corresponds to the finding in chicken skeletal muscle that the choice of exon 16 or 17 may be dependent on developmental stages. Finally, a sequence is observed corresponding to an extra exon or exons between exons 5 and 6. This sequence is shorter than that of the chicken skeletal muscle gene and is not detected in the rat skeletal muscle gene.