An extracellular endo-1,4-beta-xylanase with specific activity of 566 U/mg was purified from the culture filtrate of a filamentous fungus, Aspergillus japonicus strain MU-2, grown on oat spelt xylan. The purified enzyme showed a single band on SDS-PAGE with an apparent M-r of 25.1 kDa. Xylanase activity was optimal at pH 5.0 and 60 degrees C. The xylanase gene (xynA) encoded a 42 residue prepropeptide and a 191 residue mature protein. The XynA protein showed the highest sequence identity of 69% to Aspergillus niger XynB (DQ174549), which belongs to the glycoside hydrolase family 11. (C) 2009, The Society for Biotechnology, Japan. All rights reserved.