Fig. 1

a Physical map of the part of the rpf gene cluster from rpfB to rpfG in Xanthomonas campestris and Stenotrophomonas maltophilia K279a. The organization of ORFs predicted by sequence analysis together with predicted directions of transcription are indicated by the broad arrows. The positions of the experimentally determined transcriptional start sites in X. campestris together with the predicted transcripts are shown as single arrows. The sequence data for S. maltophilia were produced by the S. maltophilia K279a Sequencing Group at the Sanger Institute and can be obtained from http://www.sanger.ac.uk/Projects/S_maltophilia/). b DSF activity in culture supernatants of strains of S. maltophilia K279a and X. campestris. Extracts were assayed using a Xanthomonas bioassay in which restoration of endoglucanase activity to an rpfF mutant is measured (i). Introduction of the rpfF gene from S. maltophilia K279a restores the synthesis of protease to the rpfF mutant of X. campestris (ii). Enzyme activity was assessed by zones of clearing produced after growth of bacteria on skimmed milk agar plates. Top panel: Protease production in X. campestris wild-type (Xcc 8004). Middle panel: Protease production in X. campestris rpfF mutant (Xcc ∆pfF). Right panel: Protease production by Xcc ∆pfF carrying the S. maltophilia rpfF gene cloned in pLAFR3