NusA is a key component in both prevention and enhancement of transcriptional termination. It is important in both Rho-dependent and intrinsic termination, as well as in lambda and other phage antitermination systems. The gene was first identified by isolation of the nusAl mutation, which restricts bacteriophage l growth by preventing the antitermination activity of the l N protein. NusA is involved in transcriptional antitermination in the cell. It has been shown to specifically aid in read-through of the RNA polymerase genes rpoB and rpoC, as well as in successful synthesis of the ribosomal RNA genes.