1. The mRNA for a chitoporin that transports chitosugars into cells, called chiP (alias ybfM)

2. A sRNA which regulates the chitoporin post-transcriptionally, called chiX (alias sroB, micM)

3. A trap-sRNA which is transcribed from intergenic region in the chitobiose operon

(chbBCARG), which we named chiXR for chiX regulator.

Chitobiose; a disaccharide derived from chitin.

The sRNA (chiX) regulates chitoporin (chiP) expression through binding to the Shine Dalgarno sequence on the chiP mRNA inhibiting recruitment of the 30S ribosome and altering RNA stability. When chitobiose is present, trap-sRNA (chiXR) is transcribed and its transcript binds the sRNA (chiX), relieving chitoporin repression.

Overview of the E.coli chitobiose system. When Chitooligosaccarides are absent, the chbBCARG operon and hence chiXR is not transcribed, which in turns means that chiX is free to degrade chiP. Chitoporin is not produced. When Chitooligosaccarides are present, the transcription of the chbBCARG operon is transcribed. The transcribed chiXR degrades chiX and chiP mRNA is translated. Chitoporin is produced. The figure is modified from figure 5 in[1].

References

[1] Overgaard, Martin, Jesper Johansen, Jakob Møller‐Jensen, and Poul Valentin‐Hansen. “Switching off small RNA regulation with trap‐mRNA.” Molecular Microbiology 73, no. 5 (September 2009): 790-800. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2958.2009.06807.x/abstract.