Cooperation between small RNAs and the major ribonuclease RNase E in bacteria

Small RNAs (sRNAs) are major regulators of gene expression in bacteria. Traditionally, sRNAs were considered mainly as regulators of translation, exerting their regulatory function by base pairing with their target mRNAs, and through this, blocking or exposing the ribosome binding site. However, accumulating evidence suggest that sRNAs not only regulate translation, but also affect the transcript stability by assisting or interfering with endoribonuclesaes. While cooperation of sRNAs with endoribonuclesaes was demonstrated for a few genes, its extent in the bacterial cell was not assessed in large scale. Here, we take advantage of large-scale RNA-seq-based approaches to study the extent of cooperation between sRNAs with the major endoribonuclease in Escherichia coli, RNase E. As a model sRNA, we use the well-known sRNA GcvB, a sRNA that regulates genes involved in amino acid metabolism and transport. To study the cooperation between GcvB and RNase E we apply the mutant cycle approach to four strains of E. coli: wt; GcvB mutant/RNase E wt; GcvB wt/RNase E mutant; GcvB mutant/RNase E mutant. By applying RNA-seq and differential gene expression analysis, we infer different modes of cooperation between RNase E and GcvB, and show that a statistically significant number of GcvB targets are downregulated by cooperation between the two regulators. Furthermore, using the TIER-seq approach to map RNase E cleavage sites transcriptome-wide and analysing them in view of GcvB binding sites, we attempt to infer the mechanisms of cooperation between the two regulators.