Integrative promoter cloning plasmid vectors for<i>Rhizobium meliloti</i>

Cytochrome c heme lyases encoded by the Sinorhizobium meliloti cycHJKL operon are responsible for generating the covalent bond between the heme prosthetic group and apocytochromes c. The CycH protein with its presumably membrane-associated N-terminal and periplasmic C-terminal parts is thought to be responsible for binding apocytochrome and presenting it to the heme ligation machinery. We propose that these two modules of CycH play roles in different functions of the protein. The N-terminal 96 amino acids represent an active subdomain of the protein, which is able to complement the protoporphyrin IX (PPIX) accumulation phenotype of the cycH mutant strain AT342, suggesting that it is involved in the final steps of heme C biosynthesis. Furthermore, three tetratricopeptide (TPR) domains have been identified in the C-terminal periplasmic region of the CycH protein. TPR domains are known to mediate protein-protein interactions. Each of these CycH domains is absolutely required for protein function, since plasmid constructs carrying cycH genes with in-frame TPR deletions were not able to complement cycH mutants for their nitrate reductase (Rnr-) and nitrogen-fixing (Fix-) phenotypes. We also found that the 309-amino acid N-terminal portion of the CycH, which includes all the TPR domains, is able to mediate the assembly of the c-type cytochromes required for the Rnr+ phenotype. In contrast, only the full-length protein confers the ability to fix nitrogen.

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The roles of different regions of the CycH protein in c-type cytochrome biogenesis in Sinorhizobium meliloti

Cinege

Kereszt

Kertész

et al. 2004

Mol Genet Genomics

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Integrative plasmid vector for constructing single-copy reporter systems to study gene regulation in Rhizobium meliloti and related species

Ferenczi

Ganyu

Blaha

et al. 2004

Plasmid

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The ntrPR Operon of Sinorhizobium meliloti Is Organized and Functions as a Toxin-Antitoxin Module

Bodogai¹,

Ferenczi²,

Bashtovyy³

et al. 2006

MPMI

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The chromosomal ntrPR operon of Sinorhizobium meliloti encodes a protein pair that forms a toxin-antitoxin (TA) module, the first characterized functional TA system in Rhizobiaceae. Similarly to other bacterial TA systems, the toxin gene ntrR is preceded by and partially overlaps with the antitoxin gene ntrP. Based on protein homologies, the ntrPR operon belongs to the vapBC family of TA systems. The operon is negatively autoregulated by the NtrPNtrR complex. Promoter binding by NtrP is weak; stable complex formation also requires the presence of NtrR. The N-terminal part of NtrP is responsible for the interaction with promoter DNA, whereas the C-terminal part is required for protein-protein interactions. In the promoter region, a direct repeat sequence was identified as the binding site of the NtrPNtrR complex. NtrR expression resulted in the inhibition of cell growth and colony formation; this effect was counteracted by the presence of the antitoxin NtrP. These results and our earlier observations demonstrating a less effective downregulation of a wide range of symbiotic and metabolic functions in the ntrR mutant under microoxic conditions and an increased symbiotic efficiency with the host plant alfalfa suggest that the ntrPR module contributes to adjusting metabolic levels under symbiosis and other stressful conditions.

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Integrative promoter cloning plasmid vectors forRhizobium meliloti

Cited by 8 publications

References 15 publications

The roles of different regions of the CycH protein in c-type cytochrome biogenesis in Sinorhizobium meliloti

The roles of different regions of the CycH protein in c-type cytochrome biogenesis in Sinorhizobium meliloti

Integrative plasmid vector for constructing single-copy reporter systems to study gene regulation in Rhizobium meliloti and related species

The ntrPR Operon of Sinorhizobium meliloti Is Organized and Functions as a Toxin-Antitoxin Module

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