Cell division in higher plants: A cdc2 gene, its 34-kDa product, and histone H1 kinase activity in pea

The mitotic cell cycle of yeast and animal cells is regulated by the cdc2 gene and its product, the p34 protein kinase, and by other components of the MPF or histone H1 kinase complex. We present evidence that cdc2, p34, and a histone H1 kinase also exist in higher plants. Protein extracts from 10 plant species surveyed display a 34-kDa component recognized by a monoclonal antibody directed against an evolutionarily conserved epitope of fission yeast p34. Nondenatured protein extracts of mitotic Pisum sativum (garden pea) tissues were fractionated by gel filtration, electrophoretically separated under denaturing conditions, and immunoblotted. p34 crossreactive material was apparent in both low and high molecular mass fractions, indicating that pea p34 occurs as both a monomer and as part of a high molecular mass complex. Histone H1 kinase activity was found predominantly in the higher molecular mass fractions, those to which the least phosphorylated form of pea p34 was confined. We also report the cloning of the pea homologue of cdc2 by polymerase chain reaction. DNA sequence analysis reveals perfect conservation of the hallmark "PSTAIR" sequence motif found in all cdc2 gene products analyzed to date.