Fig. P1.

Posttranscriptional interaction between the core and horizontally acquired genome through Hfq and sRNAs. The SgrS sRNA is encoded by the Salmonella core genome and conserved in many bacterial species, including E. coli and Salmonella. Aided by the RNA chaperone Hfq, SgrS reduces the expression of mRNAs encoding for sugar transport proteins (ptsG and manXYZ), both of which are core genomic elements. SgrS also represses the sopD mRNA, which encodes a Salmonella virulence factor and was acquired by HGT (i.e., transfer from another organism). In contrast, SgrS does not repress the duplicated sopD2 mRNA, a process that is mediated by discrimination between G-C (sopD) and G-U (sopD2) base-pairing.