Interplay of regulatory RNAs and mobile genetic elements in enteric pathogens

Horizontal transfer of genetic information is a major driving force of evolution. In bacteria, genome plasticity is intimately linked to the ability of the bacterium to integrate novel material into existing gene expression circuits. Small RNAs (sRNAs) are a versatile class of regulatory molecules, and have recently been discovered to perform important tasks in the interplay between core genomic elements and horizontally-acquired DNA. Together with auxiliary proteins such as the RNA-chaperone Hfq and cellular ribo-nucleases, sRNAs typically act post-transcriptionally to either promote or restrict the expression of multiple target genes. Bacterial sRNAs have been identified in core and peripheral (acquired) genome sequences, and their target suites may likewise include genes from both locations. In this review, we discuss how sRNAs influence the expression of foreign genetic material in enterobacterial pathogens, and outline the processes that foster the integration of horizontally-acquired RNAs into existing regulatory networks. We also consider potential benefits and risks of horizontal gene transfer for RNA-based gene regulation.