title: Mitotic regulation of protein phosphatases by the fission yeast sds22 protein.
abstract: BACKGROUND
  Cell cycle progression requires the activity of protein kinases and phosphatases at critical points in the cell cycle in all eukaryotes. We have previously reported that the dis2(+) and sds2(+) genes of fission yeast encode redundant catalytic subunits of a type 1-like protein phosphatase. The sds22(+) gene was shown to be essential for cell viability and to interact genetically with dis2(+) and sds21(+).
  
  
  RESULTS
  Here we show by immunoprecipitation that the sds22 protein physically interacts with the dis2 and sds21 proteins, and that sds22-associated phosphatase activity has altered substrate specificity, The loss of sds22 function by a temperature sensitive mutation leads to cell cycle arrest at mid-mitosis, at which point cdc2-dependent histone Hl kinase activity is high while sds22-dependent H1 phosphatase activity is low. To examine the unusual properties of sds22 protein structure, we analyzed a collection of sds22 deletion and point mutants by a variety of functional criteria.
  
  
  CONCLUSIONS
  We propose that sds22 is a regulatory subunit of the dis2/sds21 phosphatase catalytic subunits and that sds22-bound phosphatase carries a key phosphatase activity essential for the progression from metaphase to anaphase. Mutational analysis indicates that dis2/sds21 interacts with the central repetitive domain of sds22, while the C-terminal and central regions of sds22 may be involved in subcellular targeting and the N-terminus is important for stability.
authors.affiliation: Department of Biophysics, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606, Japan.
authors.forename: E M
authors.initials: EM
authors.lastname: Stone
authors.forename: H
authors.initials: H
authors.lastname: Yamano
authors.forename: N
authors.initials: N
authors.lastname: Kinoshita
authors.forename: M
authors.initials: M
authors.lastname: Yanagida