Description
Cyclins, regulatory subunits, which associate with kinases, control many of the important steps in cell cycle progression. The Cdc2 protein kinase (p34Cdc2) exhibits protein kinase activity in vitro and exists in a complex with both cyclin B and a protein homologous to p13SUC1. Cdc2 kinase is the active subunit of the M phase promoting factor (MPF) and the M phase-specific Histone H1 kinase. The p34Cdc2/cyclin B complex is required for the G2 to M transition. An additional cell cycle-dependent protein kinase, termed p55cdc, exhibits a high degree of homology with the S. cerevisiae proteins Cdc20 and Cdc4. The p55cdc transcript is readily detectable in a variety of cultured cell lines in growth phase, but disappears when cell growth is chemically arrested