THE 14-3-3-PROTEINS ENCODED BY THE BMH1 AND BMH2 GENES ARE ESSENTIAL IN THE YEAST SACCHAROMYCES-CEREVISIAE AND CAN BE REPLACED BY A PLANT HOMOLOG

The 14-3-3 proteins comprise a family of highly conserved acidic prote ins. Several activities have been ascribed to these proteins, includin g activation of tyrosine and tryptophan hydroxylases in the presence o f calcium/calmodulin-dependent protein kinase II, regulation of protei n kinase C, phospholipase A, activity, stimulation of exocytosis and a ctivation of bacterial exoenzyme S (ExoS) during ADP-ribosylation of h ost proteins. In addition, a plant 14-3-3 protein is present in a G-bo x DNA/protein-binding complex. Previously, we isolated the BMH1 gene f rom Saccharomyces cerevisiae encoding a putative 14-3-3 protein. Using the polymerase chain reaction method, we have isolated a second yeast gene encoding a 14-3-3 protein (BMH2). While disruption of either BMH 1 or BMH2 alone had little effect, it was impossible to obtain viable cells with both genes disrupted. The cDNA encoding a plant 14-3-3 prot ein under the control of the inducible GAL1 promoter complemented the double disruption. Transfer of the complemented double disruptant to a medium with glucose resulted in the appearance of a high percentage o f large budded cells. After prolonged incubation, these cells became e nlarged with irregular buds and chains of cells defective in cell-cell separation became visible. These results suggest an essential role of the 14-3-3 proteins, possibly at a later stage of the yeast cell cycl e.