The S-box element is a riboswitch that controls different genes of sulphur metabolism in response to the presence of S-adenosylmethionine.

Upon binding of SAM, the riboswitch adopts a terminator structure resulting in transcription termination.
In the absence of SAM, the riboswitch has the antitermination structure that allows transcription elongation into the controlled gene/ operon.
S-box riboswitch turnover is initiated by RNase Y PubMed

Genes controlled by a S-box

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