Screening of genes involved in isooctane tolerance in Saccharomyces cerevisiae by using mRNA differential display

A Saccharomyces cerevisiae strain, KK-211, isolated by the long-term biopro cess of stereoselective reduction in isooctane, showed extremely high toler ance to the solvent, which is toxic to yeast cells, but, in comparison with its wild-type parent, DY-1, showed low tolerance to hydrophilic organic so lvents, such as dimethyl sulfoxide and ethanol. In order to detect the isoo ctane tolerance-associated genes, mRNA differential display (DD) was employ ed using mRNAs isolated from strains DY-1 and KK-211 cultivated without iso octane, and from strain KK-211 cultivated with isooctane. Thirty genes were identified as being differentially expressed in these three types of cells and were classified into three groups according to their expression patter ns. These patterns were further confirmed and quantified by Northern blot a nalysis. On the DD fingerprints, the expression of 14 genes, including MUQ1 , PRY2, HAC1, AGT1, GAC1, and ICT1 (YLR099c) was induced, while the express ion of the remaining 16 genes, including JEN1, PRY1, PRY3, and KRE1, was de creased, in strain KK-211 cultivated with isooctane. The genes represented by HAC1, PRY1, and ICT1 have been reported to be associated with cell stres s, and AGT1 and GAC1 have been reported to be involved in the uptake of tre halose and the production of glycogen, respectively. MUQ1 and KRE1, encodin g proteins associated with cell surface maintenance, were also detected. Ba sed on these results, we concluded that alteration of expression levels of multiple genes, not of a single gene, might be the critical determinant for isooctane tolerance in strain KK-211.