SuhB

''suhB'', also known as ''mmgR'' (makes more granules regulator), is a non-coding RNA found multiple times in the ''Agrobacterium tumefaciens'' genome and related alpha-proteobacteria. Other non-coding RNAs uncovered in the same analysis include '' speF'', '' ybhL'', ''metA'', and ''serC''.

Several studies in '' Sinorhizobium meliloti'' showed that the ''suhB'' element is indeed a non-coding RNA. It was first detected by Northern blot and called ''Sm8RNA'', then in an RNAseq study and referred to as ''SmelC689''.

The mutant (lacking the small RNA) phenotype's cytoplasm contains a higher content of polyhydroxybutyrate (PBH) storage granules than the wild type strain. The sRNA is required to limit the PBH intracellular accumulation when the nitrogen-fixing '' Sinorhizobium meliloti'' is converting surplus carbon to nitrogen ^{his needs to be modified, carbon cannot be converted to nitrogen/sup>. Further study confirmed that ''suhB'' fine-tunes the regulation of PBH storage.}

Northern blot confirmed the expression of the sRNA in other rhizobia species. ''suhB'' homologues were found in most alpha-proteobacteria. The Rho-independent terminator and a single-stranded region 10-mer (UUUCCUCCCU) are completely conserved. Hence, it was proposed to define a new family of alpha-proteobacterial sRNA, alpha-r8, of which ''suhB'' is a member.

RNA binding protein Hfq binds and stabilises ''suhB''. Expression of the mmgR gene was shown to be controlled by nitrogen (N). Further study has shown that the regulatory proteins NtrC may be required for expression of the ''suhB'' gene upon N limitation. Under carbon (C) limitation, ''suhB'' transcription is repressed by AntiA.

''suhB'' is also present in ''Sphingopyxis granuli'' strain TFA, an alpha-proteobacterium that uses the solvent tetralin as an energy source ( and references therein). ''suhB'' has been detected as a 61 nt long sRNA by Northern blot in TFA cells growing at high rates. β-galactosidase activity of a ''PsuhB::lacZ'' fusion confirmed the lower expression of ''suhB'' in TFA cells growing at low rates. A mutant lacking ''suhB'' expresses the ''thn'' genes (tetralin degradation) even in the presence of a preferential carbon source (catabolite repression conditions). This phenotype is due to the release of the negative effect of ''suhB'' on ThnR translation. Hfq is also involved in the interaction between ''suhB'' and the 5′ UTR ''thnR'' mRNA, which results in ''thn'' gene repression in catabolite repression conditions.

See also

* EcpR1 sRNA
* RcsR1 small RNA

References

External links

*

Non-coding RNA

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