Protein and DNA sequence data were obtained from the National Center for Biotechnology Information (www.ncbi.nlm.nih.gov), the Institute for Genomic Research (www.tigr.org), and the University of Wisconsin E. coli Genome Project (www.genome.wisc.edu). Protein sequence identifiers are listed in Table 2 . Sequences containing and surrounding the catalytic core of the proteases were aligned with the ClustalX algorithm (default parameters) (bips.u-strasbg.fr/fr/Documentation/ClustalX) [52] , manually edited with Genedoc (www.psc. [53] . Secondary structures were predicted with JPred (www.compbio.dundee.ac.uk/,www-jpred/) [54] . Phylograms were constructed with the MEGA software package [55] , using the Neighbor-Joining Method with Poisson correction (all substitutions, homogeneous pattern, c-distribution 2.0) and pairwise deletion of gaps. Figure 1 shows a consensus tree based on 100 bootstrap replications.