Abstract
Sequence analysis of the Helicobacter pylori major sigma factor (RpoD) shows that it is highly divergent, which may be related to the marked diversity of the H. pylori chromosome. Furthermore, the rate of divergence of RpoD among other gram-negative bacteria is much greater than that among gram-positive bacteria. This suggests that RpoD from gram-negative bacteria is functionally less constrained than that from gram-positive bacteria.