ALPHA-FORMS AND BETA-FORMS OF THE 65-KDA SUBUNIT OF PROTEIN PHOSPHATASE-2A HAVE A SIMILAR 39 AMINO-ACID REPEATING STRUCTURE

Protein phosphatase 2A (polycation-stimulated protein phosphatase L) was purified from porcine kidney and skeletal muscle. The 36-kDa catalytic and the 65-kDa putative regulatory (hereafter termed PR65) subunits of protein phosphatase 2A2 were separated by reverse-phase HPLC. Partial amino acid sequence data (300 residues) was obtained for PR65. Molecular cloning showed that two distinct mRNAs (termed α and β encoded the PR65 subunit. The cDNA encoding the α-isotype spanned 2.2 kilobases (kb) and contained an open reading frame of 1767 bases predicting a protein of 65 kDa, which was in good agreement with the size of the purified protein. The cDNAs encoding the βisotype contained an open reading frame of size similar to that of a-form but lacked an initiator ATG. Northern analysis, using RNA isolated from several human cell lines, indicated that the α-isotype was encoded by a mRNA of 2.4 kb that was much more abundant than the mRNA of 4.0 kb. Comparison of the predicted amino acid sequences of the two isotypes revealed 87% identity. The deduced protein sequences of the a- and βisotypes were found to be made up of 15 imperfect repeating units consisting of 39 amino acids. This repeating structure was conserved between species. © 1990, American Chemical Society. All rights reserved.