INDEPENDENT LIGAND-INDUCED FOLDING OF THE RNA-BINDING DOMAIN AND 2 FUNCTIONALLY DISTINCT ANTITERMINATION REGIONS IN THE PHAGE-LAMBDA N-PROTEIN

The transcriptional antitermination protein N of bacteriophage lambda binds the boxB component of the RNA enhancer nut (boxA + boxB) and the E. coli elongation factor NusA. Efficient antitermination by N requir es an RNA-binding domain (amino acids 1-22) and two activating regions for antitermination: a newly identified NusA-binding region (amino ac ids 34-47) that suppresses NusA's enhancement of termination, and a ca rboxy-terminal region (amino acids 73-107) that interacts directly wit h RNA polymerase. Heteronuclear magnetic resonance experiments demonst rate that N is a disordered protein. Interaction with boxB RNA induces only the RNA-binding domain of N to adopt a folded conformation, whil e the activating regions of the protein remain disordered in the absen ce of their target proteins.