DROSOPHILA PPY, A NOVEL MALE-SPECIFIC PROTEIN-SERINE THREONINE PHOSPHATASE LOCALIZED IN SOMATIC-CELLS OF THE TESTIS

Drosophila protein phosphatase Y (PPY) displays 64% amino acid identit y to protein serine/threonine phosphatase 1 (PP1) and 39% to protein p hosphatase 2A (PP2A). Here we show by expression of cDNA in bacteria, that PPY is a protein serine phosphatase and that its biochemical prop erties are distinct from PP1 in both substrate specificity and regulat ion by the thermostable inhibitory proteins inhibitor 1 and inhibitor 2. We also demonstrate that PPY is a novel testis specific protein pho sphatase by analysis of both mRNA and protein distribution. More preci se immunolocalisation within the testis, using affinity purified anti- PPY protein and anti-PPY peptide antibodies, shows that PPY is present in somatic cyst cells, which encase the germ cells. The predominant l ocation of PPY is in the nuclei of both head and tail cyst cells throu ghout the length of the testis except for the apical tip. The distribu tion of PPY, coupled with its unique biochemical properties, suggests that PPY may be required to prevent cyst cell division, increase trans cription for provision of nutrients to the germ cells and/or provide a signal for spermatocyte differentiation.