Post-transcriptional regulation of LPS modification. The PhoPQ TCS, a major determinant of LPS modifications, is activated in response to Mg2+ starvation as well as by antimicrobial peptides (AMPs). Translation of the phoPQ bicistronic transcript is repressed by two sRNAs, MicA and GcvB. PhoPQ controls expression of MgrR which, together with ArcZ, inhibits phosphoethanolamine (PEA) addition to the LPS oligosaccharide core by EptB. Both GcvB and MgrR are regulated at the post-transcriptional level by the sRNA SroC which acts as a sponge and induces decay of its target sRNAs. Down-regulation of lpxR mRNA by MicF decreases lipid A deacylation.