  We build a simple model for feedback systems involving small RNA (sRNA)
molecules based on the iron metabolism system in the bacterium E. coli, and
compare it with the corresponding system in H. pylori which uses purely
transcriptional regulation. This reveals several unique features of sRNA based
regulation that could be exploited by cells. Firstly, we show that sRNA
regulation can maintain a smaller turnover of target mRNAs than transcriptional
regulation, without sacrificing the speed of response to external shocks.
Secondly, we propose that a single sRNA can prioritize the usage of different
target mRNAs. This suggests that sRNA regulation would be more common in more
complex systems which need to co-regulate many mRNAs efficiently.
