Phosphatidylinositol 4-phosphate 5-kinase its3 and calcineurin Ppb1 coordinately regulate cytokinesis in fission yeast

The ppb1(+) gene encodes a fission yeast homologue of the mammalian calcine urin. We have recently shown that Ppb1 is essential for chloride ion homeos tasis, and acts antagonistically with Pmk1 mitogen-activated protein kinase pathway. In an attempt to identify genes that share an essential function with calcineurin, we screened for mutations that confer sensitivity to the calcineurin inhibitor FR506 and high temperature, and isolated a mutant, it s3-1. its3(+) was shown to be an essential gene encoding a functional homol ogue of phosphatidylinositol-4-phosphate 5-kinase (PI(4)P5K), The temperatu re:upshift or addition of FK506 induced marked disorganization of actin pat ches and dramatic increase in the frequency of septation in the its3-1 muta nts but not in: the wild-type cells. Expression of a green fluorescent prot ein-tagged Its3 and the phospholipase C delta pleckstrin homology domain in dicated plasma membrane localization of PI(4)P5K and phosphatidylinositol 4 ,5-bisphosphate. These green fluorescent protein-tagged proteins were conce ntrated at the septum of dividing cells, and the mutant Its3 was no longer localized to the plasma membrane. These data suggest that fission yeast PI( 4)P5K Its3 functions coordinately with calcineurin and plays a key role in cytokinesis, and that the plasma membrane localization of Its3 is the cruci al event in:cytokinesis.