In Aspergillusniger, the expression of genes encoding enzymes involved in the degradation of xylan and cellulose is controlled by the transcriptional regulator XlnR. Besides controlling the expression of extracellular enzymes, XlnR was shown to regulate the transcription of genes encoding intracellular enzymes as D-xylose reductase. Also the transcription of a new endoglucanase that shows major activity towards xyloglucan is controlled by XlnR. It appears that XlnR plays an extensive role in the synergistic degradation of plant cell wall polysaccharides. Transcriptional regulators as XlnR are wide spread in nature; recently XlnR orthologues have been isolated from other fungi like Aspergillus oryzae , Neurospora crassa and Trichoderma reesei . Alignment of these XlnR-like showed that several regions in the XlnR protein are highly conserved, among which the C-terminus. In A.nigerthis region was shown to fulfil a major regulatory role by controlling the activation or inactivation of XlnR.