Complex interplay of riboregulatory mechanisms at the gcvT-NGFG_01513-gcvH operon of Neisseria gonorrhoeae.

UNLABELLED: The sibling sRNAs NgncR_162 and NgncR_163 are global post-transcriptional regulators of Neisseria gonorrhoeae metabolism, which affect amino acid uptake and biosynthesis, the citric acid and methyl citric acid cycle, and in particular pathways contributing to serine-glycine metabolism. Here, we show that gcvT, gcvP, and gcvH, constituting specific components of the glycine cleavage system which converts glycine to carbon dioxide, ammonia, and 5,10-methylene tetrahydrofolate, are negatively regulated by the sibling sRNAs, while the fourth component of the GCV multienzyme complex, the L-protein, which is also involved in other cellular reactions, is not targeted by NgncR_162 and NgncR_163. In contrast to gcvP and gcvL, the expression of gcvT and gcvH, being part of a tricistronic operon, is upregulated in the presence of glycine via a translational tandem glycine riboswitch. In the absence of glycine, aptamer 2 contributes to the formation of an inhibitory secondary structure that sequesters the ribosomal-binding site of gcvT, which notably is also targeted by the sibling sRNAs. To our knowledge, this is the first example of dual control by a riboswitch and an sRNA where the same segment of the target mRNA is involved in base-pairing interactions with both the cis- and the trans-acting riboregulator, suggesting considerable structural flexibility of the gcvT-NGFG_01513-gcvH mRNA.

IMPORTANCE: In the bacterial world, riboregulation is extremely widespread and controls virtually all aspects of the life of bacterial cells. Riboregulatory mechanisms are very diverse and involve trans- and cis-acting regulatory elements such as small RNAs and riboswitches that are able to control gene expression by direct binding of small molecules. Here, we report a very peculiar and rare example of riboregulation in which an mRNA is regulated by both trans-acting sibling sRNAs and a glycine-responsive tandem riboswitch, which control glycine metabolism of the human pathogen Neisseria gonorrhoeae. This regulatory interplay of sibling sRNAs with a tandem riboswitch allows integration of different cellular signals and represents an intriguing new facet of riboregulation.