BASIDIOMYCETOUS RAS CDNA FUNCTIONALLY REPLACES ITS HOMOLOG GENES IN YEAST

It was shown by a plasmid exchange procedure that the Pas-encoding cDN A of the basidiomycete Lentinus edodes (named Leras cDNA) can function ally replace its homolog genes (ScRAS1 and ScRAS2) in the yeast Saccha romyces cerevisiae to maintain the viability of an yeast strain contai ning genetic disruptions of both RAS genes. The strain replaced by a L eras-cDNA-carrying plasmid, however, grew slower than the strains repl aced by a ScRAS1- or a ScRAS2-carrying plasmid. The intracellular leve l of cAMP in the strain harboring the Leras-cDNA-carrying plasmid was clearly higher than that of a parental strain which maintains a plasmi d carrying the S. cerevisiae cAMP-dependent protein kinase catalytic s ubunit C-1 gene, TPK1, but was lower than that in a strain harboring a n ScRAS2-carrying plasmid. These results suggest that the Leras cDNA c an complement the ras(1-) ras(2-) mutation of yeast by virture of the stimulation of adenylate cyclase activity, although the complementatio n is not as efficient as that obtained by expressing the ScRAS2 gene.