Two cDNAs for possible splicing variants of a 74-kDa regulatory subunit (B″ or δ) of human protein phosphatase 2A, were isolated. These variants were identified from human cerebral cortex by library screening and PCR, and designated δ1 and δ3 isoforms, while the previously reported isoform [Tanabe et al. (1996) FEBS Lett. 379, 107-111] was designated δ2. Compared with the δ2 isoform, the δ1 isoform contained a 32-residue insertion beginning at residue δ4, and consisted of 602 amino acids in all. The δ3 isoform lacked a 74-residue sequence corresponding to residues 1083 of the δ2 isoform, and consisted of 496 amino acids. Using isoform-specific antipeptide antisera, the 74-kDa subunit (B″ or δ) originally purified from human erythrocytes was identified as the δ1 isoform.
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