CLONING OF BOVINE MUSCLE GLYCOGEN-PHOSPHORYLASE CDNA AND IDENTIFICATION OF A MUTATION IN CATTLE WITH MYOPHOSPHORYLASE DEFICIENCY, AN ANIMAL-MODEL FOR MCARDLES-DISEASE

Genetic defects of myophosphorylase in humans cause a metabolic myopat hy (McArdle's disease) characterized by exercise intolerance, cramps, and recurrent myoglobinuria. Recently, a breed of cattle with myophosp horylase deficiency has been identified: this is the first animal mode l of McArdle's disease. To define the molecular genetic error in the c attle, we cloned and sequenced the wild-type bovine myophosphorylase c DNA. Homology to human cDNA is 95.8% for the amino acid sequence, and 92.0% for the nucleotide sequence. Sequence homology to rabbit cDNA is 97.3% in amino acid, 90.8% in nucleotide. In the cDNA fragments ampli fied by RT-PCR from muscle RNA of the cattle with myophosphorylase def iciency, we identified a C-to-T substitution, changing an encoded argi nine (CGG) to tryptophan (TGG) at codon 489. The mutant residue is adj acent to pyridoxal phosphate binding sites and to an active site resid ue, and the sequence around tills mutation is highly conserved in diff erent species.