C-protein, a myosin binding protein, is thought to regulate and stabilize thick filaments during assembly of sarcomeric A-bands. Multiple isoforms of C-protein have been characterized in avian and mammalian systems. We now report the isolation and the nucleic acid sequence of a partial C-protein cDNA clone from an axolotl heart cDNA expression library in lambda gt11. The clone was isolated by screening the library with a heterologous monoclonal anti-C-protein antibody (MF1). Sequence comparison revealed that CPRO(Axocard)1 has an average sequence identity of 62-68% at the nucleic acid and 72-78% at the amino acid levels respectively to human and chicken sequences. We could not detect any significant differences at the levels of expression of the cardiac isoform of C-protein (CPRO(Axocard)1) in normal and non-beating heart tissues of the double-recessive cardiac lethal mutant (c/c) axolotl, Ambystoma mexicanum. This is the first report of a C-protein sequence from an amphibian species. (C) 1995 Academic Press, Inc.