Striated muscle preferentially expressed genes alpha and beta are two serine/threonine protein kinases derived from the same gene as the aortic preferentially expressed gene-1

Aortic preferentially expressed gene (APEG)-1 is a 1.4-kilobase pair (kb) m RNA expressed in vascular smooth muscle cells and is down-regulated by vasc ular injury. An APEG-1 5'-end cDNA probe identified three additional isofor ms. The 9-kb striated preferentially expressed gene (SPEG)alpha and the 11- kb SPEG beta were found in skeletal muscle and heart. The 4-kb brain prefer entially expressed gene was detected in the brain and aorta. We report here cloning of the Il-kb SPEG beta cDNA SPEG beta encodes a 355-kDa protein th at contains two serine/threonine kinase domains and is homologous to protei ns of the myosin light chain kinase family. At least one Kinase domain is a ctive and capable of autophosphorylation. In the genome, all four isoforms share the middle three of the five exons of APEG-1, and they differ from ea ch other by using different 5'- and S'-ends and alternative splicing. We sh ow that the expression of SPEG alpha and SPEG beta is developmentally regul ated in the striated muscle during C2C12 myoblast to myotube differentiatio n in vitro and cardiomyocyte maturation in vivo. This developmental regulat ion suggests that both SPEG alpha and SPEG beta can serve as sensitive mark ers for striated muscle differentiation and that they may be important for adult striated muscle function.