A Consensus of Cyclin Sequences Reveals Homology with the ras Oncogene

Cyclins are universal cell cycle regulators. They were detected and named because of their cyclical accumulation and disappearance during the cell cycle (Evans et al. 1983). Indeed, abrupt mitotic destruction was originally considered the defining characteristic of a cyclin. However, additional commonalities were soon identified. Cyclins bind and activate the p34cdc2 kinase (Draetta et al. 1989; Labbé et al. 1989; Gautier et al. 1990). Furthermore, cyclin proteins share sequence similarities. Recognition of these structural and functional relationships led to new ways of identifying cyclins and consequently to expansion and diversification of the cyclin family.