A novel cyclin, CycJ18, was isolated by complementation of GI cyclin-deficient budding yeast with an Avabidopsis cDNA library. CycJ18 shares only 20% identity in its conserved cyclin box domain with other cyclins, and is predominantly expressed in young seedlings. CycJ18 is a member of a potential new plant cyclin class. (C) 2001 Elsevier Science B.V. All rights reserved.