The highly radiation-resistant bacterium Deinococcus radiodurans responds to gamma radiation or desiccationthrough the coordinated expression of genes belonging to Radiation and Desiccation Resistance/Response(RDR) regulon. RDR regulon is operated through cis-acting sequence RDRM (Radiation DesiccationResponse Motif), trans-acting repressor DdrO and protease IrrE (also called PprI). The present study evaluatedwhether RDR regulon controls the response of D. radiodurans to various other DNA damaging stressors, towhich it is resistant, such as UV rays, mitomycin C (MMC), methyl methanesulfonate (MMS), ethidiumbromide (EtBr), etc. Activation of 3 RDR regulon genes (ddrB, gyrB and DR1143) was studied by taggingtheir promoter sequences with a highly sensitive GFP reporter. Here we demonstrated that all the DNAdamaging stressors elicited activation of RDR regulon of D. radiodurans in a dose-dependent and RDRM-/IrrE-dependent manner. However, ROS-mediated indirect effects [induced by hydrogen peroxide (H2O2),methyl viologen (MV), heavy metal/metalloid (zinc or tellurite), etc.] did not activate RDR regulon. We alsoshowed that level of activation was inversely proportional to cellular abundance of repressor DdrO. Our datastrongly suggests that direct DNA damage activates RDR regulon in D. radiodurans.
Volume 46, 2020
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