DBF2 PROTEIN-KINASE BINDS TO AND ACTS THROUGH THE CELL-CYCLE-REGULATED MOB1 PROTEIN

The DBF2 gene of the budding yeast Saccharomyces cerevisiae encodes a cell cycle-regulated protein kinase that plays an important role in th e telophase/G(1) transition, As a component of the multisubunit CCR4 t ranscriptional complex, DBF2 is also involved ire the regulation of ge ne expression, We have found that MOB1, an essential protein required fur a late mitotic event in the cell cycle, genetically and physically interacts with DBF2. DBF2 binds MOB1 in vivo and can bind it in vitro in the absence of other yeast proteins, We found that the expression of MOB1 is also cell cycle regulated, its expression peaking slightly before that of DBF2 at the G(2)/M boundary, while overexpression of DB F2 suppressed phenotypes associated with mob1 temperature-sensitive al leles, it could not suppress a mob1 deletion, In contrast, overexpress ion of MOB1 suppressed phenotypes associated with a dbf2-deleted strai n and suppressed the lethality associated with a dbf2 dbf20 double del etion, A mob1 temperature-sensitive allele with a dbf2 disruption was also found to be synthetically lethal, These results are consistent wi th DBF2 acting through MOB1 and aiding in its function, Moreover, the ability of temperature-sensitive mutated versions of the MOB1 protein to interact with DBF2 was severely reduced, confirming that binding of DBF2 to MOB1 is. required for a late mitotic event, While MOB1 and DB F2 were found to be capable of physically associating in a complex tha t: did not include CCR4, MOB1 did interact with other components of th e CCR4 transcriptional complex. We discuss models concerning the role of DBF2 and MOB1 in controlling the telophase/G(1), transition.