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Barbara Ramšak, Ulrich Kück

• Fungal mating-type loci (\(\it MAT\)) encode transcription factors (TFs) MAT1-1-1 and MAT1-2-1, which govern sexual reproduction as well as other developmental processes. In \(\textit {Penicillium chrysogenum}\), the major producer of the beta-lactam antibiotic penicillin, a recent chromatin immunoprecipitation followed by sequencing (ChIP-seq) analysis identified 254 genes as direct targets of MAT1-1-1, many of which encode thus far uncharacterized proteins. Here, we characterized one of the major targets of MAT1-1-1, the \(\it tom1\) gene, which encodes a protein highly conserved within the group of Eurotiomycetes fungi. Using fluorescence microscopy, we demonstrated binding of MAT1-1-1 to the \(\it tom1\) promoter by reporter gene analysis. Extensive electrophoretic mobility shift assays (EMSAs) further showed that the promoter sequence of \(\it tom1\) is bound \(\textit {in vitro}\) by both MAT1-1-1 and MAT1-2-1. This indicated an interaction between the two TFs, which was verified by yeast two-hybrid analysis. The sequence of \(\it tom1\) carries a nuclear localization sequence, and indeed its nuclear localization was verified by fluorescence microscopy. The \(\textit {in vivo}\) function of \(\it tom1\) was investigated using \(\it tom1\) deletion strains, as well as a complementing strain where the wild-type \(\it tom1\) gene was reintroduced. We found a clear sporulation defect in the deletion strain, which became more evident when the fungi were grown at an elevated temperature of 31°C.