Elevated expression of genes under the control of stress response element (STRE) and Msn2p in an ethanol-tolerance sake yeast Kyokai no. 11

The sake yeast strain Kyokai no. 11 (K11) is an ethanol-tolerant mutant of strain Kyokai no. 7 (K7), which shows higher viability in an ethanol solution than strain K7. To clarify the mechanism underlying the ethanol tolerance of this strain, the gene expression profiles of K7 and K11 were analyzed using DNA microarrays. The results indicate that many genes induced by stresses were highly expressed in strain K11 not exposed to stresses. Analysis of HSP12, one of the most highly expressed genes in strain K11 compared with strain K7, revealed that a trans-acting factor of strain K11 was involved in the elevated expression of HSP12. Many of the highly expressed genes in strain K11 including HSP12 were under the control of a cis-acting factor called the stress response element (STRE). The addition of STRE sequences to a promoter region of a reporter gene resulted in constitutive high-level expression in strain K11. It was reported that transcription factors Msn2p and Msn4p bind to STRE sequences. DNA sequence analyses of MSN2 and MSN4 of strains K7 and K11 revealed that only Msn2p was functional in these strains. When two copies of MSN2 in strain K11 were disrupted, the expression level of the reporter gene under the control of STRE decreased to the level of strain K7, indicating that Msn2p is required for the elevated expression of the STRE-controlled genes in K11.