Isolation and analysis of xlnR, encoding a transcriptional activator co‐ordinating xylanolytic expression in Aspergillus niger

Abstract

Complementation by transformation of an Aspergillus niger mutant lacking xylanolytic activity led to the isolation of the xlnR gene. The xlnR gene encodes a polypeptide of 875 amino acids capable of forming a zinc binuclear cluster domain with similarity to the zinc clusters of the GAL4 superfamily of transcription factors. The XlnR‐binding site 5′‐GGCTAAA‐3′ was deduced after electrophoretic mobility shift assays, DNase I footprinting and comparison of various xylanolytic promoters. The 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′ consensus sequence is found within several xylanolytic promoters of various Aspergillus species and Penicillium chrysogenum. Therefore, this sequence may be an important and conserved cis‐acting element in induction of xylanolytic genes in filamentous fungi. Our results indicate that XlnR is a transcriptional activator of the xylanolytic system in A. niger.