Molecular structure of the C beta catalytic subunit of rat cAMP-dependent protein kinase and differential expression of C alpha and C beta isoforms in rat tissues and cultured cells.

A full-length cDNA clone encoding the C beta catalytic subunit of cAMP-dependent protein kinase (PKA) was isolated from a rat brain cDNA library. A 1.1 kb cDNA containing the entire coding region encodes for a protein of 351 amino acids that shows more than 95% sequence homology to the C beta subunits in mouse, bovine and human. Northern blot analysis showed distinct patterns of C alpha and C beta mRNA expression in the brain and various peripheral tissues. The C alpha mRNA was widespread and highly expressed in brain, heart, adrenal gland, testis, lung, kidney, spleen and liver, whereas the C beta mRNA was unevenly expressed in the brain and adrenal gland and in much lesser amounts in other tissues. The C alpha mRNA was evenly distributed and highly expressed through various regions of the brain, while the C beta mRNA was expressed in lesser amounts and was unevenly distributed. In neuronal and glial cultured cells, C alpha mRNA was also predominantly expressed but C beta mRNA was undetectable. The differential distribution between the C subunit isoforms of PKA suggests that individual subunits are involved in specialized functions.