Appl Microbiol Biotechnol (2012) 93:1601–1608 our unpublished data). However, glucose may not be always the best carbon source for protein production because it is known to nonenzymatically form Schiff’s bases with amino group side chains in proteins and eventually lead to their activation (Sullivan 1996). There- fore alternative carbon sources such as glycerol or protein hydrolysates, whose utilization is not XYR1 dependent could be used with probably equal results. Tef1 is known to be well expressed under all these conditions. The cdna1 promoter is currently tested by us for its response on nonglucose carbon sources. The system configured here for shake flask experiments can further be refined since conditions for highly reproducible growth of T. reesei in microtiter plates have been established which allow also the testing for the formation of extracellular enzyme activities (Seidl et al. 2006a). Taken together, our expression system based on the cDNA1- and tef1-driven expression vectors and the cellulase negative host strain Δxyr1 is suitable for a high- throughput system for testing of cellulase muteins. Acknowledgments FU and US were supported by TUBITAK (BIDEB 2210- National Scholarship Programme for MSc Students) and by the Turkish State Planning Agencies (DPT) Viskosel grant. CPK and BS were supported by the Austrian Science Foundation FWF (P19690, P19421, and P24219). Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References Akel E, Metz B, Seiboth B, Kubicek CP (2009) Molecular regulation of arabinan and L-arabinose metabolism in Hypocrea jecorina (Trichoderma reesei). 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