Control Mechanism for Production and Activation of Helicobacter pylori Urease

ABSTRACT

To define the genes for production of catalytically active H. pylori urease, we camed out study to elucidate the structure of urease gene transcript, to delineate the genetic region which affected the extent of the expression and the activation of urease structural subunits. UreC and ureD were confirmed not to affect the expression of structural genes and active enzyme production, meaning that these genes are not components of the urease gene cluster of H. pylori. p-independent transcriptional stop signal was found in 12 bp down-stream of ureH stop codon. RNA extension test showed that the transcript starts with 267 bp upstream of ureA start codon. Although accessory genes did not affect the extent of the expression of the structural subunits, they were essential for assembling the active urease in E. coli. E. coli transformants of plasmid clones containing ureAB produced catalytically active urease when they are complemented with the plasmid clones of ureIEFGH or coexisted with ureIEFGH, meaning that accessory gene products could be trans-acting as well as cis-acting. The extent of production of urease structural subunits depended on the region of 241 to 57 bp upstream of ureA start codon. E. coli transformant of pBeloBACII clone containing the urease gene cluster, which is maintained with a single copy in host, did not express the urease. Proteins (60, 38, 30, 29, 27, and 24 kDa) that could hold nickel ions were identified in the cell extract of H. pylori. The results in this study will provide the basis to understand the control mechanism for urease gene expression and formation of the active urease.