ISOLATION AND ANALYSIS OF XLNR, ENCODING A TRANSCRIPTIONAL ACTIVATOR COORDINATING XYLANOLYTIC EXPRESSION IN ASPERGILLUS-NIGER

Complementation by transformation of an Aspergillus niger mutant lacki ng xylanolytic activity led to the isolation of the xlnR gene. The xln R gene encodes a polypeptide of 875 amino acids capable of forming a z inc binuclear cluster domain with similarity to the zinc clusters of t he GAL4 superfamily of transcription factors. The XlnR-binding site 5' -GGCTAAA-3' was deduced after electrophoretic mobility shift assays, D Nase I footprinting and comparison of various xylanolytic promoters. T he importance of the second G within the presumed XlnR binding site 5' -GGCTAAA-3' was confirmed in vitro and in vivo. The 5'-GGCTAAA-3' cons ensus sequence is found within several xylanolytic promoters of variou s Aspergillus species and Penicillium chrysogenum. Therefore, this seq uence may be an important and conserved cis-acting element in inductio n of xylanolytic genes in filamentous fungi. Our results indicate that XlnR is a transcriptional activator of the xylanolytic system in A. n iger.