NsiR4 (nitrogen stress-induced RNA 4), former name SyR12, is a cyanobacterial non-coding RNA which plays role in the regulation of Glutamine synthetase (GS), a key enzyme in biological nitrogen assimilation. NsiR4 interacts with the 5′UTR of the mRNA of the GS inactivating factor IF7 ("gifA" mRNA) and reduces its expression. NsiR4 expression is under positive control of the nitrogen control transcription factor (NtcA). NsR4 is a first example of an sRNA controlling the assimilation of a micronutrient.
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