Drosophila contains three genes that encode distinct isoforms of protein phosphatase 1

Abstract

The sequences of two Drosophila and one rabbit protein phosphatase (PP) 1 catalytic subunits were determined from their cDNA. The sequence of Drosophila PP1α1 was deduced from a 2.2‐kb cDNA purified from an embryonic cDNA library, while that for Drosophila PP1β was obtained from overlapping clones isolated from both a head cDNA library and an eye imaginal disc cDNA library. The gene for Drosophila PP1α1 is at 96A2–5 on chrõmosome 3 and encodes a protein of 327 amino acids with a calculated molecular mass of 37.3 kDa. The gene for Drosophila PP1β is localized at 9C1–2 on the X chromosome and encodes a protein of 330 amino acids with a predicted molecular mass of 37.8 kDa. PP1α1 shows 96% amino acid sequence identity to PP1α2 (302 amino acids), an isoform whose gene is located in the 87B6–12 region of chromsome 3 [Dombrádi, V., Axton, J. M., Glover, D. M. Cohen, P. T. W. (1989) Eur. J. Biochem. 183, 603–610]. PP1β shows 85% identity to PP1α1 and PP1α2 over the 302 homologous amino acids. These results demonstrate that at least three genes are present in Drosophila that encode different isoforms of PP1. Drosophila PP1α1 and PP1β show 89% amino acid sequence identity to rabbit PP1α (330 amino acids) [Cohen, P. T. W. (1988) FEBS Lett. 232, 17–23] and PP1β (327 amino acids), respectively, demonstrating that the structures of both isoforms are among the most conserved proteins known throughout the evolution of the animal kingdom. The presence of characteristic structural differences between PP1α and PP1β, which have been preserved from insects to mammals, implies that the α and β isoforms may have distinct biological functions.