Maltotriose is the second most abundant fermentable sugar in wort and, due to incomplete fermentation, residual maltotriose in beer causes both quality and economic problems in the brewing industry. To identify genes that might improve utilization of maltotriose, we developed a library containing genomic DNA from four lager strains and a laboratory Saccharomyces cerevisiae strain and isolated transformants that could grow on YP/2% maltotriose in the presence of 3 mg/l of the respiratory inhibitor antimycin A. In this way we found a gene which shared 74% similarity with MPH2 and MPH3, 62% similarity with AGT1 and 91% similarity with MAL61 and MAL31, all encoding known maltose transporters. Moreover, the gene shared an even higher similarity (98%) with the uncharacterized Saccharomyces pastorianus mty1 gene (M. Salema-Oom, unpublished; NCBI Accession No. AJ491328). Therefore, we named the gene MTT1 (mty1-like transporter). We showed that the gene was present in four different lager strains but was absent from the laboratory strain CEN.PK113-7D. The ORF in the plasmid isolated from the library lacks 66 base pairs from the 3 -end of MTT1 but instead contains 54 bp of the vector. We named this ORF MTT1alt (NCBI Accession No. DQ010174).14 C-Maltose and repurified 14 C-maltotriose were used to show that MTT1 and, especially, MTT1alt, encode maltose transporters for which the ratio between activities to maltotriose and maltose is higher than for most known maltose transporters. Introduction of MTT1 or MTT1alt into lager strain A15 raised maltotriose uptake by about 17% or 105%, respectively.

A DNA-encoded small-molecule library was prepared using yoctoReactor technology followed by binder trap enrichment to identify selective inhibitors with nanomolar potencies against p38α MAP kinase.

The significance of COMPASS on silencing of the FLO and MAL genes, located close to telomeres, was studied in different Saccharomyces cerevisiae strains that fermented high concentrations of maltose (20%) with different efficiency. In one particular fast maltose-fermenting yeast strain, with constitutive expression of FLO11, the expression of FLO1, FLO5 and FLO9 was induced during fermentation of high concentrations of maltose or glucose. In another strain the expression of mainly FLO1 was induced. Mutants of these strains with a defective COMPASS, however, formed very large aggregates of cells earlier in the fermentation and more pronounced than the wild-type. The formation of the large flocs was dependent on calcium ions and was inhibited by mannose. The flocculation displayed by mutants defective in COMPASS was due to increased amounts of FLO1, FLO5 and FLO9 transcripts. COMPASSmediated silencing of the MAL genes was detected at the later stages of fermentation in strains that fermented high concentrations of maltose slowly and incompletely, while silencing was not detectable in strains that fermented maltose fast. Thus, COMPASS, in addition to the MAL genes, is also involved in silencing the expression of the FLO1, FLO5 and FLO9 genes.

Maltose transporter genes were isolated from four lager yeast strains and sequenced. All four strains contain at least two different types of maltose transporter genes, MTT1 and MAL31. In addition, 'long' 2.7 kb, and 'short' 2.4 kb, versions of each type exist. The size difference is caused by the insertion of two repeats of 147 bp into the promoter regions of the long versions of the genes. As a consequence of the insertion, two Mal63-binding sites move 294 bp away from the transcription initiation site. The 2.4- and 2.7-kb versions are further highly similar. Only the 2.4-kb versions and not the 2.7-kb versions of MTT1 could restore the rapid growth of lager yeast strain A15 on maltotriose in the presence of antimycin A. These results suggest that insertion of the two repeats into the promoter region of the 'long versions' of MTT1 genes led to a diminished expression of these genes. None of the tested long and short versions of the MAL31 genes were able to restore this growth. As the promoter regions of the MTT1 and MAL31 genes are identical, small differences in the protein sequence may be responsible for the different properties of these genes.

The performance of yeast is often limited by the constantly changing environmental conditions present during high-gravity fermentation. Poor yeast performance contributes to incomplete and slow utilization of the main fermentable sugars which can lead to flavour problems in beer production. The expression of the FLO and MAL genes, which are important for the performance of yeast during industrial fermentations, is affected by complex proteins associated with Set1 (COMPASS) resulting in the induction of flocculation and improved maltose fermentation capacity during the early stages of high-gravity fermentation. In this study, we investigated a possible role for other histone modifying proteins. To this end, we tested a number of histone deacetylases (HDACs) and histone acetyltransferases and we report that flocculation is induced in absence of the histone deacetylase Hda1 or the histone acetyltransferase Gcn5 during high-gravity fermentation. The absence of Gcn5 protein also improved utilization of high concentrations of maltose. Deletion of SIR2 encoding the HDA of the silent informator regulator complex, did not affect flocculation under high-gravity fermentation conditions. Despite the obvious roles for Hda1 and Gcn5 in flocculation, this work indicates that COMPASS mediated silencing is the most important amongst the histone modifying components to control the expression of the FLO genes during high-gravity fermentation.