Nus Factors of Escherichia coli.

Abstract

The Nus factors-NusA, NusB, NusE, and NusG-area set of well-conserved proteins in bacteria and are involved in transcription elongation, termination, antitermination, and translation processes. Originally, Escherichia coli host mutations defective for supporting bacteriophage λ N-mediated antitermination were mapped to the nusA (nusA1), nusB (nusB5, nusB101), and nusE (nusE71) genes, and hence, these genes were named nus for Nutilization substances (Nus). Subsequently,the Nus factors were purified and their roles in different host functions were elucidated. Except for NusB, deletion of which is conditionally lethal, all the other Nus factors are essential for E. coli. Among the Nus factors, NusA has the most varied functions. It specifically binds to RNA polymerase (RNAP), nascent RNA, and antiterminator proteins like N and Q and hence takes part in modulating transcription elongation, termination, and antitermination. It is also involved in DNA repair pathways. NusG interacts with RNAP and the transcription termination factor Rho and therefore is involved in both factor-dependent termination and transcription elongation processes. NusB and NusE are mostly important in antitermination at the ribosomal operon-transcription. NusE is a component of ribosome and may take part in facilitating the coupling between transcription and translation. This chapter emphasizes the structure-function relationship of these factors and their involvement in different fundamental cellular processes from a mechanistic angle.