Construction of two new vectors for transformation of laboratory, natural and industrial Saccharomyces cerevisiae strains to trifluoroleucine and G418 resistance.

Two new plasmids, pEC3 and pECkan, were constructed and their use in yeast transformation described. Both plasmids are derivative of the pRS416 vector, in which the URA3 auxotrophic marker was replaced by the LEU4* gene (pEC3) or the kanMX4 gene (pECkan). pEC3 and pECkan plasmids transformed natural and commercial Saccharomyces cerevisiae strains to 5,5,5-trifluoro-DL-leucine and G418 (aminoglycoside related to gentamicin) resistance, respectively, with efficiency ranging from 10(-5) to 10(-7) transformants per number of viable cells. pEC3 transformed the Leu- laboratory strain, carrying the mutations leu4 leu9, to leucine prototrophy with efficiency of approximately 10(-4).