Escherichia coli protease VII (EC 3.4.21.87) (omptin) (gene ompT) [1] is an outer-membrane associated protease with a specificity for paired basic residues. It seems to be an aspartyl protease [2] inhibited by zinc ions. Omptin is highly similar to the following proteins:

• Salmonella typhimurium outer membrane protease E (gene pgtE) [3], also specific for paired basic residues.
• Yersinia pestis coagulase/fibrinolysin (plasminogen activator) (gene pla) [4]. This enzyme is encoded on a plasmid required for the pathogenic potential of the bacteria. It cleaves and activates plasminogen at the foci of infection; this allows plasmin to degrade fibrin barriers thus promoting the invasiveness of the plague bacteria.
• Escherichia coli outer membrane protease ompP [5].

The mature forms of these enzymes are proteins of about 280 to 300 amino-acid residues. As signature patterns, we selected two well conserved regions in the central part of these proteins.