An improved tetracycline-inducible expression vector for Staphylococcus aureus.

The tetracycline-inducible expression vector pALC2073 allowed high level expression of the cloned sasG gene but repression by uninduced cells was leaky. The -10 box of the tetR promoter was mutated to the Bacillus subtitlis consensus, which resulted in complete repression of SasG protein expression. Anhydrotetracycline at 1.28 microg ml(-1) gave the same high level of induction that was obtained with pALC2073sasG using 160 ng ml(-1) tetracycline, the highest concentration that could be used without inhibiting bacterial growth. This variant of pALC2073 thus offers almost complete repression when uninduced and high levels of expression when induced.