Two endo-beta-1,4-xylanase-encoding genes were amplified from Aspergillus niger ATCC 90196 mRNA, inserted between the yeast ADH2 promoter and terminator sequences (genes designated XYN4 and XYN5) and expressed in Saccharomyces cerevisiae. The nucleotide sequences of the XYN4 and XYN5 genes revealed that both genes encode 211-amino acid proteins that are 92% identical to each other. Both the Xyn4 and Xyn5 enzymes have pH and temperature optima of pH 4 and 60 degrees C, respectively. Autoselective S. cerevisiae strains were developed that allowed beta-xylanase production and secretion in complex medium.