Figure 3. ArnR and ArnR1 are phosphorylated by ArnC.

(A) Sequence alignment of S. solfataricus (Sso) ArnR and S. acidocaldarius (Saci) ArnR and ArnR1. Location of HTH (Helix-turn-Helix, green), HAMP (Histidine kinases, Adenyl cyclases, Methyl-accepting proteins and Phosphatases), sensor (orange) and transmembrane domain (blue) are depicted (Lassak et al., 2013). Saci_ArnR1 phosphorylation sites Tyr217 and Thr222 as identified in vivo are depicted in pink (Reimann et al., 2013) and Sso ArnR phosphorylation sites Tyr154 and Tyr155 are depicted in yellow (Esser et al., 2012). (B and C) In vitro phosphorylation assay. one µM ArnC (B) or ArnD (C) was incubated with µM ArnR or ArnR1 and y³²-p-ATP and phosphotransfer from ArnC or ArnD to ArnR and ArnR1 was monitored, respectively. A representative phosphoimage of three independent experiments is shown.