Transmembrane orientation and receptor-like structure of the Rhizobium meliloti common nodulation protein NodC.
The 46.8-kd NodC protein of Rhizobium meliloti is a membrane protein, essential for nodule formation. Gene fusions of nodC to a portion of the lambda cI repressor gene were used to define the membrane-anchor domain which is necessary for membrane insertion of the NodC protein into the membrane. The transmembrane orientation of NodC was confirmed by surface-specific radiolabeling and proteolysis experiments. A highly hydrophobic transmembrane-anchor domain was found near the carboxyl terminus, separating a large extracellular domain which contains an unusual cysteine-rich cluster from a short putative intracellular domain. Cross-linking studies showed that the NodC protein exists in the membrane probably as a dimer. The domain structure of the NodC protein shows striking similiarities with cell surface receptors. In nodules of various legumes a truncated form of the NodC protein was detected. The processed NodC was associated with the bacteroids and the amount of this protein increased during nodule development.
John
M
M
Max-Planck-Institut für Züchtungsforschung, Abteilung Schell, D-5000 Köln 30, FRG.
Schmidt
J
J
Wieneke
U
U
Krüssmann
H D
HD
Schell
J
J