2 NOVEL FAMILIES OF BACTERIAL-MEMBRANE PROTEINS CONCERNED WITH NODULATION, CELL-DIVISION AND TRANSPORT

Homology has been established for members of two families of functiona lly related bacterial membrane proteins. The first family (the resista nce/nodulation/ cell division (RND) family) includes (i) two metal-res istance efflux pumps in Alcaligenes eutrophus (CzcA and CnrA), (ii) th ree proteins which function together in nodulation of alfalfa roots by Rhizobium meliloti (NoIGHI), and (iii) a cell division protein in Esc herichia coli (EnvD). The second family (the putative membrane fusion protein (MFP) family) includes a nodulation protein (NoIF), a cell div ision protein (EnvC), and a multidrug resistance transport protein (Em rA). We propose that an MFP functions co-operatively with an RND prote in to transport large or hydrophobic molecules across the two membrane s of the Gram-negative bacterial cell envelope.