ChIP-Seq of the Sinorhizobium meliloti CRP-like protein Clr in combination with either cAMP or cGMP under different growth conditions
In bacteria, Crp-Fnr superfamily transcription factors mediate 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) signaling. The CRP-like protein Clr of the soil-dwelling and plant-symbiotic a-proteobacterium Sinorhizobium meliloti was previously shown to activate target promoters in both its cAMP- and cGMP-bound states (Krol et al., Microbiology 62:1840–1856, 2016). In order to further characterize the overall regulon of Clr in S. meliloti Chromatin Immuno Precipitation DNA-Sequencing (ChIP-Seq) experiments were performed with C-terminally FLAG tagged Clr under four different growth conditions, namely growth in TY complex medium and MOPS minimal medium, each supplemented with either cAMP or cGMP. For each condition, the respective immunoprecipitated (IP) and non-immunoprecipitated (control) samples were analyzed and compared to locate genomic positions in which Clr-DNA binding occurs. In combining ChIP-Seq with Electrophoretic Mobility Shift Assays and promoter-probe assays we expanded the list of known Clr-regulated target promoters and showed that virtually all of these promoters containing a palindromic Clr binding site (CBS) motif are activated both by Clr•cAMP and Clr•cGMP.