CLONING OF THE XYNNB GENE ENCODING XYLANASE-B FROM ASPERGILLUS-NIGER AND ITS EXPRESSION IN ASPERGILLUS-KAWACHII

Aspergillus niger IFO 4066 produced two xylanases, xylanase A (XynNA) and xylanase B (XynNB), in culture medium, and these enzymes were puri fied. Acidophilic xylanase such as xylanase C (XynC) of white koji mol d (Aspergillus kawachii IFO 4308) was not detected in A. niger culture s. However, results of Southern analysis using xynC cDNA of A. kawachi i as a probe suggested that A. niger contained a gene homologous to xy nC of A. kawachii. Therefore, we cloned this xylanase gene from A. nig er. The predicted amino acid sequence of the cloned xylanase showed a homology to that of xynC of A. kawachii. However, a large number of am ino acid substitutions were detected, especially in the N-terminal reg ion. Both this cloned gene and xynC gene of A. kawachii had an intron at the same position in the coding region. The cloned gene was express ed in A. kawachii and a large quantity of xylanase was produced. The e lution profile on an anion exchange chromatogram and the N-terminal am ino acid sequence of the xylanase purified from the transformant were the same as those of XynNB. This confirmed that the cloned gene encode d XynNB.