AUTHOR=Álvarez-Escribano Isidro , Vioque Agustín , Muro-Pastor Alicia M. 

TITLE=NsrR1, a Nitrogen Stress-Repressed sRNA, Contributes to the Regulation of nblA in Nostoc sp. PCC 7120

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.02267

DOI=10.3389/fmicb.2018.02267

ISSN=1664-302X

ABSTRACT=<p>Small regulatory RNAs (sRNAs) are currently considered as major post-transcriptional regulators of gene expression in bacteria. The interplay between sRNAs and transcription factors leads to complex regulatory networks in which both transcription factors and sRNAs may appear as nodes. In cyanobacteria, the responses to nitrogen availability are controlled at the transcriptional level by NtcA, a CRP/FNR family regulator. In this study, we describe an NtcA-regulated sRNA in the cyanobacterium <italic>Nostoc</italic> sp. PCC 7120, that we have named NsrR1 (<underline>n</underline>itrogen <underline>s</underline>tress <underline>r</underline>epressed <underline>R</underline>NA<underline>1</underline>). We show sequence specific binding of NtcA to the promoter of NsrR1. Prediction of possible mRNA targets regulated by NsrR1 allowed the identification of <italic>nblA</italic>, encoding a protein adaptor for phycobilisome degradation under several stress conditions, including nitrogen deficiency. We demonstrate specific interaction between NsrR1 and the 5′-UTR of the <italic>nblA</italic> mRNA, that leads to decreased expression of <italic>nblA</italic>. Because both NsrR1 and NblA are under transcriptional control of NtcA, this regulatory circuit constitutes a coherent feed-forward loop, involving a transcription factor and an sRNA.</p>