High-Resolution Crystal Structure of RpoS Fragment

Legionella pneumophila RpoS (LpRpoS) is an alternative sigma factor of RNA polymerase 13 (RNAP) essential for virulence and stress resistance. To investigate the mechanism of RpoS in the 14 intracellular pathogen L. pneumophila, we determined the high-resolution crystal structure of the 15 LpRpoS (residues 95-194) containing a partial region 1.2 and region 2. The structure of LpRpoS 16 (residues 95-194) reveals that the conserved residues are critical for promoter melting, DNA and 17 core RNAP binding. The differences in regulatory factor binding site between Escherichia coli RpoS 18 and LpRpoS suggest that LpRpoS may employ a distinct mechanism to recruit alternative 19 regulatory factors controlling transcription initiation. 20