Chicken cardiac tropomyosin and a low-molecular-weight nonmuscle tropomyosin are related by alternative splicing

We have isolated and characterized complementary DNAs (cDNAs) encoding chicken cardiac muscle tropomyosin and a low-molecular-weight nonmuscle tropomyosin. The cardiac muscle cDNA (pCHT-4) encodes a 284-amino acid protein that differs from chicken skeletal muscle alpha- and beta-tropomyosins throughout its length. The nonmuscle cDNA (pFT-C) encodes a 248-amino acid protein that is most similar (93-94%) to the tropomyosin class including rat fibroblast TM-4, equine platelet tropomyosin, and human fibroblast TM30pl. The nucleotide sequences of the cardiac and nonmuscle cDNAs are identical from the position encoding cardiac amino acid 81 (nonmuscle amino acid 45) through cardiac amino acid 257 (nonmuscle amino acid 221). The sequences differ both 5' and 3' of this region of identity. These comparisons suggest that the chicken cardiac tropomyosin and low-molecular-weight "platelet-like" tropomyosin are derived from the same genomic locus by alternative splicing. S1 analysis suggests that this locus encodes at least one other tropomyosin isoform.