A Xenopus total ovary cDNA library was constructed in a fission yeast expression vector. Using a genetic functional complementation method, we have identified a Xenopus cDNA clone that can rescue several different yeast mitotic catastrophe mutants defective in Wee1 kinase function at the restrictive temperature. The 3.0-kb cDNA clone contains an open reading frame (ORF) of 2226 nucleotides, encoding a predicted 82-kDa protein. The deduced amino acid (aa) sequence shows seven almost identical 30-aa tandem repeats, each of which contains a phosphorylation site meeting the consensus for both Cdc2 kinase and MAP kinase.