Phosphorylation of histone H3 at serine 10 occurs during mitosis and meiosis in a wide range of eukaryotes and has been shown to be required for proper chromosome transmission in Tetrahymena. Here we report that Ipl1/aurora kinase and its genetically interacting phosphatase, Glc7/PP1, are responsible for the balance of H3 phosphorylation during mitosis in Saccharomyces cerevisiae and Caenorhabditis elegans. In these models, both enzymes are required for H3 phosphorylation and chromosome segregation, although a causal link between the two processes has not been demonstrated. Deregulation of human aurora kinases has been implicated in oncogenesis as a consequence of chromosome missegregation. Our findings reveal an enzyme system that regulates chromosome dynamics and controls histone phosphorylation that is conserved among diverse eukaryotes.

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Mutations in the SRA1 or SRA3 gene eliminate the requirement for either RAS gene (RAS] (4,7).In this study we cloned and sequenced SRAI and SRA3 and characterized mutations constructed in them. We demonstrate that SRAI encodes the regulatory subunit and that SRA3 likely encodes the catalytic subunit of cAMPdependent protein kinase. MATERIALS AND METHODSYeast strains, plasmids, and media. The genotypes of yeast strains and plasmids are given in Table 1. The inserts of plasmids are shown in Fig. 1 and 3B. The ras2-530 mutation is a LEU2 disruption of RAS2 (45 Cloning SRAJ. KT293 was transformed (2) with a yeast genomic library constructed in YCp5O, kindly provided by Mark Rose. The approximately 5,000 Ura+ transformants were incubated in nitrogen-deficient medium (7) for 3 days at 30°C. DNA was prepared from surviving transformants (less than 0.1%) that reverted two additional sral traits: lack of glycogen accumulation and ability to allow ras2-530 mutants to grow on nonfermentable carbon sources. The plasmid p713 which reverts all these traits of sral-l was recovered.Cloning SRA3. A 10-pLg sample of EcoRI-digested JC303-54 (ras2-530 SRA4-6) chromosomal DNA was ligated to 2 ,ug of EcoRI-digested YCp50 and used to transform JC302-26B spheroplasts to Ura+ (2). After transformant colonies had grown to a diameter of 2 mm (4 days at 30°C), they were extracted from the agar, diluted, and spread on YEP-acetate plates at 37°C. DNA was prepared from transformants that grew on YEP-acetate after 4 days at 37°C. The plasmid p1017 was recovered; it allowed JC302-26B (ras2-530) transformants to grow on YEP-acetate and other nonfermentable carbon sources.DNA sequence analysis. DNA restriction fragments were cloned into M13 vectors mplO and mpll (31) and used as templates for DNA sequence determination with avian myeloblastosis virus reverse transcriptase (Bio-Rad Laboratories, Richmond, Calif., or Boehringer Mannheim Biochemicals, Indianapolis, Ind.) or the large fragment of DNA polymerase I (P-L Biochemicals, Inc., Milwaukee, Wis.) (37). We used primers complementary to the mp