Clarification: A version of Stephen J. Elledge's comment on this paper, which appeared in the Sept. 14, 1992, issue of The Scientist, contained an editing error that significantly altered its meaning. Following is a corrected version of Elledge's remarks.
S.J. Elledge and M.R. Spottswood, "A new human p34 protein kinase, CDK2, identified by complementation of a cdc28 mutation in Saccharomyces-cerevisiae, is a homolog of Xenopus Eg1," The EMBO Journal, 10:2653-9, 1991.
Stephen J. Elledge (Baylor College of Medicine, Houston): "Critical transitions in the eukaryotic cell cycle are controlled by the activity and substrate specificity of a protein kinase, p34cdc2, and its associated regulatory subunits, cyclins. In yeasts, this kinase is encoded by a single gene and is capable of regulating entry into two very different cellular states: S-phase (DNA synthesis) and M-phase (mitosis). Prior to this work, it was thought that human cells also possessed only a single CDC2-like gene, ...
