Histone-like Nucleoid-Structuring Protein (H-NS) Paralogue StpA Activates the Type I-E CRISPR-Cas System against Natural Transformation in Escherichia coli.

Working mechanisms of CRISPR-Cas systems have been intensively studied. However, far less is known about how they are regulated. The histone-like nucleoid-structuring protein H-NS binds the promoter of genes (P ) and suppresses the type I-E CRISPR-Cas system in Although the H-NS paralogue StpA also binds P , its role in regulating the CRISPR-Cas system remains unidentified. Our previous work established that is able to take up double-stranded DNA during natural transformation. Here, we investigated the function of StpA in regulating the type I-E CRISPR-Cas system against natural transformation of We first documented that although the activated type I-E CRISPR-Cas system, due to deletion, interfered with CRISPR-Cas-targeted plasmid transfer, inactivation restored the level of natural transformation. Second, we showed that inactivating reduced the transcriptional activity of P Third, by comparing transcriptional activities of the intact P and the P with a disrupted H-NS binding site in the and null deletion mutants, we demonstrated that StpA activated transcription of genes by binding to the same site as H-NS in P Fourth, by expressing StpA with an arabinose-inducible promoter, we confirmed that StpA expressed at a low level stimulated the activity of P Finally, by quantifying the level of mature CRISPR RNA (crRNA), we demonstrated that StpA was able to promote the amount of crRNA. Taken together, our work establishes that StpA serves as a transcriptional activator in regulating the type I-E CRISPR-Cas system against natural transformation of StpA is normally considered a molecular backup of the nucleoid-structuring protein H-NS, which was reported as a transcriptional repressor of the type I-E CRISPR-Cas system in However, the role of StpA in regulating the type I-E CRISPR-Cas system remains elusive. Our previous work uncovered a new route for double-stranded DNA (dsDNA) entry during natural transformation of In this study, we show that StpA plays a role opposite to that of its paralogue H-NS in regulating the type I-E CRISPR-Cas system against natural transformation of Our work not only expands our knowledge on CRISPR-Cas-mediated adaptive immunity against extracellular nucleic acids but also sheds new light on understanding the complex regulation mechanism of the CRISPR-Cas system. Moreover, the finding that paralogues StpA and H-NS share a DNA binding site but play opposite roles in transcriptional regulation indicates that higher-order compaction of bacterial chromatin by histone-like proteins could switch prokaryotic transcriptional modes.