The cell cycle then and now.

In the last few years a general model of cell cycle control has been established for all eukaryotic cells. Experiments from a variety of organisms and from a variety of experimental approaches have identified a protein kinase and its unstable regulatory subunit as the activator of mitosis; related molecules seem to be involved in the activation of chromosome replication. The identification of the biochemical components of these important regulatory pathways is providing several new insights into homeostatic and developmental control mechanisms in higher organisms.