Processive antitermination requires the complete antitermination complex. The assembly of NusB, S10, and NusG onto the core complex involves nt 2 to 7 of lambda BOXA (CGCUCUUACACA), as well as the carboxyl-terminal region of N, which interacts with RNAP. The role of NusG in the N antitermination reaction is not clear. NusG binds to termination factor Rho and to RNAP. It stimulates the rate of transcription elongation and is required for the activity of certain Rho-dependent terminators. NusG is a component of the complete antitermination complex and enhances N antitermination in vitro. However, alteration of lambda BOXA to a variant called BOXA consensus (CGCUCUUUAACA) allows NusB and S10 to assemble in the absence of NusG. Furthermore, depletion of NusG has no effect on lambda N antitermination in vivo, and unlike nusA, nusB, and nusE, no point mutations in nusG that block N activity have been isolated. A NusG homolog, RfaH, enhances elongation of several transcripts in E. coli and S. typhimurium. The possibility that RfaH and NusG are redundant for N antitermination has not yet been tested, although for several other functions, the two proteins are not interchangeable.