The structural basis for regulated assembly and function of the transcriptional activator NtrC

X-ray solution scattering and electron microscopy structures of the activated, full-length nitrogen regulatory protein C (NtrC) is reported, showing a novel mechanism for regulation of AAA+ ATPase assembly via the juxtaposition of the receiver domains and ATPase ring. Accompanying the hydrolysis cycle that is required for transcriptional activation, major order-disorder changes in the GAFTGA loops involved in the sigma(super 54) binding as well as in the DNA-binding domains are observed.