cDNA Cloning of BRγ, A Novel Brain-specific Isoform of the B Regulatory Subimit of Type-2A Protein Phosphatase

A cDNA clone for a novel isoform of the B regulatory subunit of type 2A protein phosphatase (BR) was isolated from a rat brain cDNA libraryby hybridization under low-stringency conditions with the BRβ cDNA fragment as a probe. The novel cDNA encodes a protein of 447 amino acids. The identities of amino acid sequences of the novel isoform with those of rat BRα and BRβ were 80% and 85%, respectively, with a unique sequence at the C-terminal. Since this isoform is thought to be encoded by a third gene for the B regulatory subunit, it was named BRγ. The mRNA for BRγ was 4.2 kb. The expression level of BRγ was high in the brain and spinal cord of rats, and its expression was also detected in mouse and human brains, but in contrast to BRβ, it was not detected in the testes of rats or mice. Thus BRγ is thought to be a brain-specific isoform of the B regulatory subunit.