TY - JOUR T1 - Coherent feedforward regulation of gene expression by <em>Caulobacter</em> σ<sup>T</sup> and GsrN during hyperosmotic stress JF - bioRxiv DO - 10.1101/344820 SP - 344820 AU - Matthew Z. Tien AU - Benjamin J. Stein AU - Sean Crosson Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/06/12/344820.abstract N2 - GsrN is a conserved small RNA that is under the transcriptional control of the general stress response (GSR) sigma factor, σT, and functions as a major post-transcriptional regulator of Caulobacter crescentus survival across multiple stress conditions. We have conducted molecular genetic studies aimed at defining features of GsrN structure that determine cell survival under hyperosmotic stress, and have applied biochemical, transcriptomic and proteomic methods to define molecular regulatory targets of GsrN under hyperosmotic conditions. The 5’ end of GsrN, which includes a conserved cytosine-rich stem loop structure, is necessary for cell survival upon osmotic upshock. GsrN both activates and represses gene expression when cells encounter a hyperosmotic environment. Among the genes most highly activated by GsrN is an uncharacterized open reading frame we have named osrP, which is predicted to encode a 37 kDa glycine-zipper protein. We present evidence that GsrN physically interacts with osrP mRNA through its 5’ C-rich stem loop to enhance OsrP protein expression. Given that σT directly activates gsrN and osrP transcription, and that GsrN post-transcriptionally activates OsrP protein expression, we conclude that sigT, gsrN, and osrP comprise a coherent feedforward loop. This study delineates transcriptional and post-transcriptional layers of Caulobacter gene expression control during hyperosmotic stress, uncovers a new regulatory target of GsrN, and defines a coherent feedforward motif within the Caulobacter GSR regulatory network. ER -