Generation of an ilv bradytrophic phenocopy in yeast by antisense RNA.

We report for the first time on the regulation of gene expression in yeast by antisense RNA. Chimaeric genes were constructed containing the 5' upstream and partial coding sequence of SMR1--a sulfometuron methyl resistant allele of the ILV2 locus. Such fragments were placed 5' to 3' and 3' to 5' under control of the GAL10 promoter and CYC1 terminator in a high copy YEp plasmid. Following galactose induction only transformants containing antisense RNA genes showed biological activity against SMR1 gene expression. Antisense RNA inhibited synthesis of the SMR1 gene product acetolactate synthase and thus repressed cellular growth which resulted in a bradytrophic auxotroph revertable by addition of isoleucine and valine. Antisense RNA inhibition was enhanced in galactose medium containing sulfometuron methyl and in gcn4 cells deficient for positive regulation of the ILV2 locus. This system can be used to study factors that interfere with antisense RNA function and to assign biological function to randomly cloned DNA fragments.