Here, we present the crystal structure of the cytoplasmic domain of FliF complexed with the N-terminal domain of FliG (FliF  -FliG  ) from the bacterium Helicobacter pylori Within this complex, FliF  interacted with FliG  through extensive hydrophobic contacts similar to those observed in the FliF  -FliG  structure from the thermophile Thermotoga maritima, indicating conservation of the FliF  -FliG  interaction across bacterial species.  We validated the in vivo relevance of the FliG  stacking by complementation studies in Escherichia coli Furthermore, structural comparison with apo FliG from the thermophile Aquifex aeolicus indicated that FliF regulates the conformational transition of FliG and exposes the complementary ARM-like motifs of FliG  , containing conserved hydrophobic residues. 
THERM