Functional equivalence of HMGA- and histone H1-like domains in a bacterial transcriptional factor

High-Mobility-Group A-Like CarD Binds to a DNA Site Optimized for Affinity and Position and to RNA Polymerase To Regulate a Light-Inducible Promoter in Myxococcus xanthus

“…We have found that the CarD C-terminal HMGA-like domain can be replaced with no loss of function not only by human HMGA1a but also by human histone H1 or its C-terminal region (H1-CTR) or by the domain resembling H1-CTR in the CarD ortholog found in the myxobacterium Anaeromyxobacter dehalogenans (CarD Ad ) (13). CarD Ad forms a stable complex with Car-G Ad (a CarG ortholog in A. dehalogenans) but not with M. xanthus CarG, and, despite the lower DNA binding affinity of CarD Ad relative to that of CarD in vitro, the CarD Ad -CarG Ad pair could functionally replace the CarD-CarG pair in M. xanthus (13).…”

“…CarD Ad forms a stable complex with Car-G Ad (a CarG ortholog in A. dehalogenans) but not with M. xanthus CarG, and, despite the lower DNA binding affinity of CarD Ad relative to that of CarD in vitro, the CarD Ad -CarG Ad pair could functionally replace the CarD-CarG pair in M. xanthus (13).…”

“…Through this domain CarD forms a stable complex with CarG, which is indispensable in every known CarD-dependent process (13,15). CarG has an H/C-rich zinc binding motif similar to archaemetzincin metalloproteases (15,18) but lacks protease activity and does not bind DNA directly (13,15). CarG thus appears to function as a transcriptional adaptor.…”

“…M. xanthus CarD has a C-terminal domain with four AT hooks that resembles human HMGA1a (with three AT hooks) in its physical, structural, and DNA binding properties (Fig. 1A) (13)(14)(15). In contrast to mammalian HMGA, CarD also has a structurally well-defined Nterminal domain of ϳ180 residues which is essential for function and defines the widely distributed CarD_CdnL_TRCF family of bacterial proteins or protein modules that have been implicated in interactions with RNA polymerase (RNAP) (5,(13)(14)(15)(16)(17).…”

“…In contrast to mammalian HMGA, CarD also has a structurally well-defined Nterminal domain of ϳ180 residues which is essential for function and defines the widely distributed CarD_CdnL_TRCF family of bacterial proteins or protein modules that have been implicated in interactions with RNA polymerase (RNAP) (5,(13)(14)(15)(16)(17). Through this domain CarD forms a stable complex with CarG, which is indispensable in every known CarD-dependent process (13,15). CarG has an H/C-rich zinc binding motif similar to archaemetzincin metalloproteases (15,18) but lacks protease activity and does not bind DNA directly (13,15).…”