Expression of Phaseolin cDNA Genes in Yeast under Control of Natural Plant DNA Sequences

We have constructed a strain of Saccharomyces cerevisiae that expresses two different members of the multigene family encoding phaseolin, the major seed storage glycoprotein from the French bean, Phaseolus vulgaris. Yeast vector plasmids have been engineered to include a Phaseolus DNA segment that contains the natural 5′and 3′plant genomic regulatory sequences flanking a cDNA copy of the protein-encoding region. Characterization of phaseolin transcripts isolated from transformed yeast cells revealed the presence of two classes of polyadenylylated RNA, approximately 1400 and 1800 bases, which initiate and terminate in plant DNA sequences. Protein extracts from transformants contain phaseolin-immunoreactive proteins similar in size to those isolated from plant tissue. These polypeptides are glycosylated in yeast and their molecular weights are consistent with the possibility that the phaseolin signal peptide has been cleaved to form the mature protein.