Two isoforms of protein phosphatase 1 may be produced from the same gene

A cDNA clone encoding a second type-1 protein phosphatase catalytic subunit (1 alpha) was isolated from a rabbit skeletal muscle cDNA library constructed in lambda gt10. The deduced protein sequence (330 residues, 37.5 kDa) was 19 residues longer at its N-terminus than protein phosphatase 1 beta(311 residues, 35.4 kDa). The amino acid sequences of protein phosphatases 1 alpha and 1 beta were identical after residue 33 of protein phosphatase 1 alpha. The results suggest that the different N-terminal sequences of protein phosphatases 1 alpha and 1 beta are likely to be generated by differential transcription or processing of the mRNA transcribed from a single gene. Southern blotting of rabbit DNA was consistent with this interpretation.