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The mexR gene encoded product MexR in nalB mutants of Pseudomonas aeruginosa is modified by a single amino acid that compromizes the stability of the protein or its ability to dimerize. However, modification of L95 and R21 amino acid residues confer stability and dimerization capability but compromises DNA binding.

Results show that MexR, encoded by mexR repressor gene, functions solely as a repressor and controls the multidrug expression system and 5' end of the mexR gene may be the promoter of this expression system.

Research was conducted to test whether the outer membrane OprM protein influences beta-lactam recognition and efflux in Pseudomonas aeruginosa. The oprM gene was cloned on a SphI fragment into a derivative called pXZL01 while the MexCD-OprM efflux system was constructed and analyzed for reconstitution of efflux activity. Results showed that the efflux components are highly homologous and are characterized by an integral cytoplasmic membrane component, a linker protein and an outer membrane protein.

The porin protein of Haemophilus influenzae type b was analyzed using monoclonal antibodies (Mabs) to define the epitopic regions of the outer membrane protein. The results showed that the antigenic determinants of porin are located between amino acids 162 and 172 and between 318 and 325. Based on these results, as well as on the predicted secondary structure of porin, a model for the surface topological structure of porin is presented.