Gene expression changes triggered by exposure of Haemophilus influenzae tonovobiocin or ciprofloxacin: Combined transcription and translation analysis

The responses of Haemophilus influenzae to DNA gyrase inhibitors were analy zed at the transcriptional and the translational level. High-density microa rrays based on the genomic sequence were used to monitor the expression lev els of >80% of the genes in this bacterium. In parallel the proteins were a nalyzed by two-dimensional electrophoresis. DNA gyrase inhibitors of two di fferent functional classes were used. Novobiocin, as a representative of on e class, inhibits the ATPase activity of the enzyme, thereby indirectly cha nging the degree of DNA supercoiling. Ciprofloxacin, a representative of th e second class, obstructs supercoiling by inhibiting the DNA cleavage-resea ling reaction. Our results clearly show that different responses can be obs erved. Treatment with the ATPase inhibitor Novobiocin changed the expressio n rates of many genes, reflecting the fact that the initiation of transcrip tion For many genes is sensitive to DNA supercoiling. Ciprofloxacin mainly stimulated the expression of DNA repair systems as a response to the DNA da mage caused by the stable ternary complexes. In addition, changed expressio n levels were also observed for some genes coding for proteins either annot ated as "unknown function" or "hypothetical" or For proteins not directly i nvolved in DNA topology or repair.