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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.
Gunning et al. (Thu,) studied this question.