ABSTRACT The common nodulation genes nodA, B, and C are highly conserved between different Rhizobium species and are required for the nodulation of legumes and non-legumes. The expression of these genes in Rhizobium meliloti is under both positive and negative control. Monospecific polyclonal antibodies were used to localize the NodA and NodB proteins in the cytosol of R. meliloti. These proteins are involved in the generation of small heat-stable compounds that stimulate the mitosis of different plant protoplasts. Our experiments suggest that the NodC transmembrane protein is not involved in the synthesis of these factors. Gene fusion experiments were used to define the membrane-anchor domain which is necessary for the insertion of the NodC protein into the membrane. A highly hydrophobic transmembrane-anchor domain was found near the carboxyl terminus, separating a large extracellular domain which contains a cystein-rich cluster from a short putative intracellular domain. The domain structure of the dime...
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