FIG 4.

Involvement of 2-OG and glutamine in the regulation of NifA activity by NifL and GlnK. (A) At low-2-OG concentrations, NifL forms a complex with NifA and NifA activity is inhibited. (B) At high concentrations, 2-OG (dark blue circles) binds to NifA to prevent inhibition by NifL. At low glutamine concentrations, GlnK is uridylylated and unable to interact with NifL. At high glutamine concentrations, GlnK is deuridylylated, and the nonmodified form of GlnK interacts with NifL, resulting in the formation of a ternary GlnK-NifL-NifA complex. This complex is formed even when GlnK is saturated with MgATP (magenta circles) and 2-OG (dark blue circles).