Identification of the Helicobacter pylori anti-sigma(28) factor

Flagellar motility is essential for colonization of the human gastric mucos a by Helicobacter pylori. The flagellar filament is composed of two subunit s, FlaA and FlaB. Transcription of the genes encoding these proteins is con trolled by the sigma (28) and sigma (54) factors of RNA polymerase respecti vely. The expression of flagellar genes is regulated, but no sigma (28)-spe cific effector was identified. It was also unclear whether H. pylori posses sed a checkpoint for flagellar synthesis, and no gene encoding an anti-sigm a (28) factor, FIgM, could be identified by sequence similarity searches. T o investigate the sigma (28)-dependent regulation, a new approach based on genomic data was used. Two-hybrid screening with the H. pylori proteins ide ntified a protein of unknown function (HP1122 interacting with the sigma (2 8) factor and defined the C-terminal part of HP1122 (residues 48-76) as the interaction domain. HP1122 interacts with region 4 of sigma (28) and preve nts its association with the beta -region of H. pylori RNA polymerase. Thus , HP1122 presented the characteristics of an anti-sigma (28) factor. This w as confirmed in H. pylori by RNA dot-blot hybridization and electron micros copy. The level of sigma (28)-dependent flaA transcription was higher in a HP1122-deficient strain and was decreased by the overproduction of HP1122. The overproduction of HP1122 also resulted in H. pylori cells with highly t runcated flagella. These results demonstrate that HP1122 is the H. pylori a nti-sigma (28) factor, FIgM, a major regulator of flagellum assembly. Poten tial anti-sigma (28) factors were identified in Campylobacter jejuni, Pseud omonas aeruginosa and Thermotoga maritima by sequence homology with the C-t erminal region of HP1122.