The interaction surface of a bacterial transcription elongation factor required for complex formation with an antiterminator during transcription antitermination.
ABSTRACT: The bacterial transcription elongation factor, NusA, functions as an antiterminator when it is bound to the lambdoid phage derived antiterminator protein, N. The mode of N-NusA interaction is unknown, knowledge of which is essential to understand the antitermination process. It was reported earlier that in the absence of the transcription elongation complex (EC), N interacts with the C-terminal AR1 domain of NusA. However, the functional significance of this interaction is obscure. Here we identified mutations in NusA N terminus (NTD) specifically defective for N-mediated antitermination. These are located at a convex surface of the NusA-NTD, situated opposite its concave RNA polymerase (RNAP) binding surface. These NusA mutants disrupt the N-nut site interactions on the nascent RNA emerging out of a stalled EC. In the N/NusA-modified EC, a Cys-53 (S53C) from the convex surface of the NusA-NTD forms a specific disulfide (S-S) bridge with a Cys-39 (S39C) of the NusA binding region of the N protein. We conclude that when bound to the EC, the N interaction surface of NusA shifts from the AR1 domain to its NTD domain. This occurred due to a massive away-movement of the adjacent AR2 domain of NusA upon binding to the EC. We propose that the close proximity of this altered N-interaction site of NusA to its RNAP binding surface, enables N to influence the NusA-RNAP interaction during transcription antitermination that in turn facilitates the conversion of NusA into an antiterminator.
PROVIDER: S-EPMC3784721 | BioStudies |