Primary structure of chicken skeletal muscle and fibroblast α‐actinins deduced from cDNA sequences

The complete 897‐amino‐acid sequence of chicken skeletal muscle α‐actinin and the 856‐amino‐acid sequence (97% of the entire sequence) of chicken fibroblast α‐actinin have been determined by cloning and sequencing the cDNAs. Genomic Southern analysis with the cDNA sequences shows that skeletal and fibroblast α‐actinins are encoded by separate single‐copy genes. RNA blot analyzes show that the skeletal α‐actinin gene is expressed in the pectoralis muscle and that the fibroblast gene is expressed in the gizzard smooth muscle as well as in the fibroblast. The deduced skeletal α‐actinin molecule has a calculated M_r of 104 × 10³, and each α‐actinin can be divided into three domains: (1) the NH₂‐terminal highly conserved actin‐binding domain, which shows similarity to the product of the Duchenne's muscular dystrophy locus; (2) the middle rod‐shaped dimer‐forming domain, which contains the spectrin‐type repeat units; and (3) the COOH‐terminal two EF‐hand consensus regions. Comparison of the skeletal α‐actinin sequence with the fibroblast and smooth muscle α‐actinin sequences demonstrated that the EF‐hand structure was conserved in all of these α‐actinin sequences, despite the reported variability of the Ca²⁺ sensitivities of the actin‐gelation by various α‐actinin isoforms.