Biochemistry and Molecular Biology of Protein Phosphatase 1 in Drosophila melanogaster

Protein phosphatase 1 (PP1) activity was detected with exogenous and endogenous substrates in Drosophila extract. The catalytic subunit of PP1 was purified to apparent homogeneity. The physicochemical and biochemical properties of the preparation were very similar to those of rabbit PP1. One PP1 catalytic subunit was cloned from a Drosophila cDNA library with the aid of a rabbit PP1 cDNA and oligonucleotide probes. Subsequently, three additional genes encoding for highly similar PP1 isoforms in Drosophila were identified and cloned. It was found that the primary structure of PP1 had been very well conserved during evolution. One of the isoforms, called PP1(87B), was predominantly expressed during all developmental stages of the insect. Several mutations affecting the PP1(87B) gene were characterized. Based on the phenotype of different mutant alleles, it was concluded that PP1(87B) was involved in viability, mitosis, interphase chromatin condensation and learning. Our results demonstrate that PP1(87B) has several functions which cannot be complemented by other PP1 isoforms of Drosophila