Transcriptional and mutational analysis of the Helicobacter pylori urease promoter

Urease is an essential virulence factor of the human gastric pathogen Helicobacter pylori, and is expressed to very high levels. The promoter of the urease operon contains sequences resembling the canonical -10 and extended -10 motifs, but no discernible -35 motif. To establish the role of different motifs and regions in the urease promoter, we fused the urease promoter to a genomic lacZ reporter gene in H. pylori, made substitutions in the aforementioned promoter motifs, and also made deletions in the upstream sequences removing regulatory sequences. Substitutions in the -10, extended -10 and predicted -35 motifs all significantly altered expression of the lacZ reporter gene, demonstrating their importance in transcription of the H. pylori urease operon. In contrast, sequential deletions upstream of the -35 region did not affect expression of the lacZ reporter gene. This demonstrates the modular structure of the H. pylori urease promoter, where basal levels of transcription are initiated from a typical sigma(70) promoter, which requires -10 and extended -10 motifs, and also its -35 motif for efficient transcription. Upstream sequences are not involved in basal levels of urease transcription, but play an important role in responses to environmental stimuli like nickel.