Expression of the xylan-degrading genes of Bacillus pumilus IPO in Saccharomyces cerevisiae

Xylanase (xynA) and β-xylosidase (xynB) genes of Bacillus pumilus were expressed in Saccharomyces cerevisiae by using the GAP (glyceraldehyde-3-phosphate dehydrogenase) promoter of S. cerevisiae. Yeast cells harboring a plasmid pNAX2 containing xynA produced xylanase in the cytoplasm of the cell to an extent as much as 5% of the total soluble protein in the cell extract. Xylanase produced in yeast had an extra methionine at the N-terminus, but had the same specific activity as that produced by B. pumilus IPO. The xylanase in the yeast was not glycosylated and was immunologically identical to that of B. pumilus IPO. Yeast cells harboring a plasmid pYXB containing xynB produced β-xylosidase in the cytoplasm of the cell (3% of the total soluble protein). β-Xylosidase purified from the yeast strain exhibited specific activity nearly equal to the value of enzyme purified from B. pumilus, and had an N-terminal sequence identical to the sequence of the enzyme from B. pumilus.