RsmX

RsmX is a small non-coding regulatory RNA (sRNA) found in several Pseudomonas species, most prominently in Pseudomonas aeruginosa. It forms part of the Rsm (or CsrA-like) regulatory network that controls post-transcriptional gene expression. As an sRNA, RsmX does not encode a protein; instead, it modulates gene expression by interacting with RNA-binding proteins of the RsmA family.

The primary mechanism of action involves sequestering RsmA-type proteins (and related regulators such as RsmE) away from their mRNA targets. By binding these translational repressors, RsmX relieves repression on target transcripts, influencing processes such as motility, biofilm development, secondary metabolism, and virulence factor production. RsmX typically contains multiple binding motifs, including GGA sequences, arranged in stem-loop structures that enable effective interaction with RsmA-family proteins.

Expression of RsmX is governed by the GacS/GacA two-component regulatory system, which coordinates the entire Gac regulon in response to environmental cues. Under the control of GacA, rsmX transcription is coordinated with other related sRNAs in the same regulatory circuit, notably rsmY and rsmZ, forming a layered network that fine-tunes RsmA activity and downstream gene expression.

Beyond Pseudomonas, homologous RsmX-like RNAs have been identified in related bacteria, suggesting a conserved role in CsrA-family regulation. The study of RsmX contributes to understanding how bacteria integrate environmental signals to balance planktonic growth, surface attachment, and pathogenic traits.