CDC2MSB, A COGNATE CDC2 GENE FROM ALFALFA, COMPLEMENTS THE G1/S BUT NOT THE G2/M TRANSITION OF BUDDING YEAST CDC28 MUTANTS

The product of the cdc2 gene encodes the p34cdc2 protein kinase that controls entry of yeast cells into S phase and mitosis. In higher eukaryotes, at least two cdc2-like genes appear to be involved in these processes. A cdc2 homologous gene has previously been isolated from alfalfa and shown to complement a fission yeast cdc2ts mutant. Here the isolation of cdc2MsB, a cognate cdc2gene from alfalfa (Medicago sativa) is reported. Southern blot analysis shows that cdc2MsA and cdc2MsB are present as single copy genes in different tetraploid Medicago species. cdc2MsB encodes a slightly larger mRNA (1.5 kb) than cdc2MsA (1.4 kb). Both genes were found to be expressed at similar steady state levels in different alfalfa organs. Expression levels of both cdc2Ms genes correlate with the proliferative state of the organs. Complementation studies revealed that in contrast to cdc2MsA, cdc2MsB was not able to rescue a cdc2ts fission yeast mutant. cdc2MsB was also unable to rescue a G2/M-arrested cdc28ts budding yeast mutant which could be rescued by expression of the cdc2MsA gene. Conversely, cdc2MsB but not cdc2MsA was found to complement the G1/S block of another cdc28ts budding yeast mutant. These results suggest that cdc2MsA and cdc2MsB function at different control points in the cell cycle.