The construction of a xylose-inducible expression vector is described.
This vector allows the integration of any gene, coding for its authen
tic protein, at the amyE locus of Bacillus subtilis (Bs). The controla
ble expression cassette consists of the repressor-encoding gene and th
e promoter of the Bacillus megaterium-derived operon for xylose utiliz
ation, sandwiched between the 5'- and 3'-ends of amyE. This thereby al
lows insertion of in vitro constructed transcriptional fusions at the
amyE locus of the Bs chromosome. The versatility of this expression sy
stem was tested by fusing three different heat-shock genes to the xylo
se-inducible promoter and following their expression by Western immuno
blot analysis. Whereas no increase in the amount of heat-shock protein
could be detected under non-inducing conditions when compared to the
isogenic wild-type strain, the three proteins were strongly induced af
ter addition of xylose, depending on the gene. To determine the tightn
ess and the induction factor of the system more accurately, the bgaB g
ene encoding a heat-stable beta-galactosidase (beta Gal) was analyzed.
The background activity of beta Gal increased by a factor of at least
200 after addition of xylose. The system is not subject to catabolite
, but rather to glucose repression.