RHIZOBIUM-ETLI CYCHJKL GENE LOCUS INVOLVED IN C-TYPE CYTOCHROME BIOGENESIS - SEQUENCE-ANALYSIS AND CHARACTERIZATION OF 2 CYCH MUTANTS

The cycHJKL gene locus was cloned from Rhizobium etli by the rescue of a Tn5mob insertion of a mutant (IFC01) which was affected in the prod uction of c-type cytochromes. The cycH, cycJ, cycK and cycL genes are proposed to code for different subunits of a haem lyase complex involv ed in the attachment of haem to cytochrome c apoproteins. CycH of 365 aa shared 27, 36, 47 and 63% identity with CycH from Paracoccus denitr ificans, Bradyrhizobium japonicum, R meliloti, and R. leguminosarum, r espectively. CycJ of 153 aa shared 52, 71, and 85% identity to the cyc J gene product of B. japonicum, R meliloti, R. leguminosarum, respecti vely. CycK of 666 at shared 62, 73, and 90% homology with CycK from B. japonicum, R meliloti, and R. leguminosarum respectively, while CycL of 151 aa shared 57, 67 and 86% homology with CycL from the abovementi oned species. The Tn5mob insertion present in the IFC01 strain was loc ated in the cycH gene. This strain was able to infect bean plants, but unable to fix nitrogen during symbiosis. A previously described R etl i cytochrome c-deficient MuD1lac-induced mutant (CFN4202) that induced empty nodules on Phaseolus vulgaris, also have lesions in cycH. Compl ementation analysis suggested that the MuD1lac insertion of the CFN420 2 strain was polar on expression of genes downstream of cycH in contra st with the Tn5mob insertion present in IFC01, which showed no polarit y on cycJKL. Our data suggest that CycH may not be essential for the i nfection process, but is necessary for nitrogen fixation. (C) 1998 Els evier Science B.V.