In order to reproduce itself a cell must grow, replicate its DNA and divide. Some of the processes involved are continuous, whereas others are one-off processes which need to be highly coordinated and tightly regulated, if cells are to grow and divide successfully, only when it is appropriate to do so. A consequence of this is tha different cells progress through the cell cycle at different rates, in response to external and internal signals.
Fission yeast is a simple unicellular eukaryote which provides a powerful tool for genetic studies.
These CDC genes are highly conserved through evolution, and homologous mammalian genes have been identified using genetic complementation of mutant yeast strains. 1 Frog oocytes, eggs and embryos have been used to identify, assay and characterise MPF and its biological activity. Yeast temperature sensitive mutants have also been used to isolate structurally and functionally homologous mammalian CDC genes. For example, p21CIP1 a KIP-type inhibitor helps to bring about the cell cycle arrest following DNA damage. The tumour suppressor protein p53 is involved in mediating this inhibition by upregulating p21CIP1 expression.