CLONING OF 4 CYCLINS FROM MAIZE INDICATES THAT HIGHER-PLANTS HAVE 3 STRUCTURALLY DISTINCT GROUPS OF MITOTIC CYCLINS

While a large number of cyclins have been described in animals and yea sts, very limited information is available regarding cyclins in plants . We describe here the isolation of cDNA clones encoding four putative mitotic cyclins from maize. All four cyclins were able to induce matu ration of Xenopus oocytes, demonstrating that they can act as mitotic cyclins in this system. Northern analysis showed that all four cyclins were expressed only in actively dividing tissues and organs, with a s tronger correlation between expression and mitotic activity than is ob served with cdc2. The deduced protein sequences suggest that the four maize cyclins belong to the cyclin A and B families identified from an imal and yeast studies but that they cannot be described easily as eit her A-type or B-type cyclins. However, comparison with previously clon ed plant cyclins shows that cyclins in higher plants form three distin ct structural groups that have been conserved in both monocotyledonous and dicotyledonous species and that cyclins from all three groups are present within a single plant species.