Enterobacterial H-NS-like proteins and Pseudomonas MvaT-like proteins share low homology at the amino acid sequence level, but both can function as xenogeneic silencers and are included in the H-NS family of proteins. H-NS family members have dimerization/oligomerization and DNA-binding domains connected by a flexible linker and form large nucleoprotein complexes using both domains. Pmr, an MvaT-like protein encoded on the IncP-7 carbazole-degradative plasmid pCAR1, is a key regulator of an interaction between pCAR1 and its host Pseudomonas putida KT2440. KT2440 has two transcribed genes that encode the MvaT-like proteins TurA and TurB. Our previous transcriptome analyses suggested that the functions of Pmr, TurA and TurB are non-equivalent, although the detailed underlying mechanisms remain unclear. In this study, we focused on the protein–protein interactions of Pmr, and assessed the homo-oligomerization capacity of various substituted and truncated Pmr derivatives by protein–protein cross-linking analysis. Six of the seven residues identified as important for homo-oligomerization in Pmr were located near the N-terminus, and the putative flexible linker or the region near that was not involved in homo-oligomerization, suggesting that Pmr homo-oligomerization is different from that of enterobacterial H-NS and that the functional mechanism differs between H-NS-like and MvaT-like proteins. In addition, we assessed homo- and hetero-oligomerization of Pmr by surface plasmon resonance analysis and found that the coupling ratio of TurB-Pmr oligomers is smaller than that of Pmr-Pmr or TurA-Pmr oligomers. These results raised the possibility that composition of the hetero-oligomers of Pmr, TurA, and TurB could explain why the different gene sets were affected by either pmr, turA, or turB disruption in our previous studies.

H-NS family proteins play key roles in bacterial nucleoid compaction and global transcription. MvaT homologues in Pseudomonas have almost negligible amino acid sequence identity with H-NS, but can complement an hns-related phenotype of Escherichia coli. Here, we report the crystal structure of the N-terminal dimerization/oligomerization domain of TurB, an MvaT homologue in Pseudomonas putida KT2440. Our data identify two dimerization sites; the structure of the central dimerization site is almost the same as the corresponding region of H-NS, whereas the terminal dimerization sites are different. Our results reveal similarities and differences in dimerization and oligomerization mechanisms between H-NS and TurB.

The redox-responsive regulator SurR in the hyperthermophilic archaea Pyrococcus furiosus and Thermococcus kodakarensis binds to the SurR-binding consensus sequence (SBS) by responding to the presence of elemental sulfur. Here we constructed a surR gene disruption strain (DTS) in T. kodakarensis, and identified the genes that were under SurR control by comparing the transcriptomes of DTS and parent strains. Among these genes, transcript levels of ferredoxin:NADP oxidoreductases 1 and 2 (FNOR1 and FNOR2) genes displayed opposite responses to surR deletion, indicating that SurR repressed FNOR1 transcription while enhancing FNOR2 transcription. Each promoter region contains an SBS upstream (uSBS) and downstream (dSBS) of TATA. In addition to in vitro binding assays, we examined the roles of each SBS in vivo. In FNOR1, mutations in either one of the SBSs resulted in a complete loss of repression, indicating that the presence of both SBSs was essential for repression. In FNOR2, uSBS indeed functioned to enhance gene expression, whereas dSBS functioned in gene repression. SurR bound to uSBS2 of FNOR2 more efficiently than to dSBS2 in vitro, which may explain why SurR overall enhances FNOR2 transcription. Further analyses indicated the importance in the distance between uSBS and TATA for transcriptional activation in FNOR2.