Chromosomal location of the co-expressed human skeletal and cardiac actin genes

We have examined the relationship between chromosomal location and regulation of the two human genes encoding the sarcomeric muscle actins. The human genes encoding skeletal alpha-actin and cardiac alpha-actin are co-expressed in both human skeletal muscle and heart. We have subcloned a single-copy DNA fragment from an intervening sequence in the human cardiac alpha-actin gene and a single-copy DNA sequence from the 3' untranslated region of a human skeletal alpha-actin cDNA. Using these two gene-specific probes, we examined DNA isolated from human-mouse somatic cell hybrid lines segregating human chromosomes. We observed the segregation of restriction endonuclease-generated DNA cleavage fragments that hybridize to the two probes. The two striated muscle genes do not co-segregate and are on different autosomes. The human cardiac alpha-actin gene (ACTC) is on chromosome 15 in the q11----qter region whereas the skeletal alpha-actin gene (ACTSK) is on chromosome 1 in the p21----qter region. The co-expression of these two genes is not a function of chromosomal linkage. Neither of these muscle genes can be the primary target resulting in X-linked muscular dystrophies.