THE LARGEST SUBUNITS OF RNA-POLYMERASE FROM GASTRIC HELICOBACTERS ARETETHERED

The rpoB and rpoC genes of eubacteria and archaea, coding respectively for the beta- and beta'-like subunits of DNA-dependent RNA polymerase , are organized in an operon with rpoB always preceding rpoC. The geno me sequence of the gastric pathogen Helicobacter pylori (strain 26695) revealed homologs of two genes in one continuous open reading frame t hat potentially could encode one 2890-amino acid-long beta-beta' fusio n protein. Here, we show that this open reading frame does in fact enc ode a fused beta-beta' polypeptide. In addition, we establish by DNA s equencing that rpoB and rpoC are also fused in each of four other unre lated strains of H. pylori, as well as in Helicobacter felis, another member of the same genus. In contrast, the rpoB and rpoC genes are sep arate in two members of the related genus Campylobacter (Campylobacter jejuni and Campylobacter fetus) and encode separate RNA polymerase su bunits. The Campylobacter genes are also unusual in overlapping one an other rather than being separated by a spacer as in other Gramnegative bacteria. We propose that the unique organization of rpoB and rpoC in H. pylori may contribute to its ability to colonize the human gastric mucosa.