RT Journal Article SR Electronic(1) A1 Ruiz, Diego A1 Salinas, Paloma A1 Lopez-Redondo, Maria Luisa A1 Cayuela, Maria Luisa A1 Marina, Alberto A1 Contreras, AsunciónYR 2008 T1 Phosphorylation-independent activation of the atypical response regulator NblR JF Microbiology, VO 154 IS 10 SP 3002 OP 3015 DO https://doi.org/10.1099/mic.0.2008/020677-0 PB Microbiology Society, SN 1465-2080, AB Cyanobacteria respond to environmental stress conditions by adjusting their photosynthesis machinery. In Synechococcus sp. PCC 7942, phycobilisome degradation and other acclimation responses after nutrient or high-light stress require activation by the orphan response regulator NblR, a member of the OmpR/PhoB family. Although NblR contains a putative phosphorylatable residue (Asp57), it lacks other conserved residues required to chelate the Mg2+ necessary for aspartic acid phosphorylation or to transduce the phosphorylation signal. In close agreement with these features, NblR was not phosphorylated in vitro by the low-molecular-mass phosphate donor acetyl phosphate and mutation of Asp57 to Ala had no impact on previously characterized NblR functions in Synechococcus. On the other hand, in vitro and in vivo assays show that the default state of NblR is monomeric, suggesting that, despite input differences, NblR activation could involve the same general mechanism of activation by dimerization present in known members of the OmpR/PhoB family. Structural and functional data indicate that the receiver domain of NblR shares similarities with other phosphorylation-independent response regulators such as FrzS and HP1043. To acknowledge the peculiarities of these atypical ‘two-component’ regulators with phosphorylation-independent signal transduction mechanisms, we propose the term PIARR, standing for phosphorylation-independent activation of response regulator., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.2008/020677-0