A PROTEIN PHOSPHATASE-1 FROM ARABIDOPSIS-THALIANA RESTORES TEMPERATURE SENSITIVITY OF A SCHIZOSACCHAROMYCES-POMBE CDC25TS WEE1- DOUBLE MUTANT

There is increasing evidence that the mechanisms controlling the eukar yotic cell cycle are regulated by protein phosphorylation/dephosphoryl ation cascades. The catalytic subunit of the protein phosphatase 1 is implicated genetically and biochemically in the complex network that r egulates mitosis. To investigate further the cell division in plants, we have isolated and characterized two full-length cDNAs from Arabidop sis thaliana, PP1A-At1 and PP1A-At2, encoding polypeptides highly homo logous to known protein phosphatase 1 (PP1). DNA gel blot analysis sug gests that the protein phosphatases 1 might form a small gene family i n Arabidopsis. Northern analysis shows that transcripts are present in all plant organs. In cell cultures, the PP1 mRNA levels are different ially affected by treatment with drugs that block cell division. The e xpression of PP1A-At1 in a Schizosaccharomyces pombe cdc25ts/wee1- dou ble-mutant strain restores temperature sensitivity, showing that the A rabidopsis phosphatase gene is capable of interacting with genes that regulate the fission yeast mitotic apparatus. However, the dis2-11 S. pombe strain, which has a cold-sensitive allele of the phosphatase 1 g ene, is not rescued by expression of the PP1A-At1 gene, suggesting tha t the plant cDNA is not a functional homolog of the fission yeast gene .