Part of the processive rRNA transcription and antitermination complex (rrnTAC). The complex forms an RNA-chaperone ring around the RNA exit tunnel of RNA polymerase (RNAP). It supports rapid transcription and antitermination of rRNA operons, cotranscriptional rRNA folding, and annealing of distal rRNA regions to allow correct ribosome biogenesis (PubMed:32871103). Participates in both transcription termination and antitermination. Involved in a variety of cellular termination and antitermination processes, such as Rho-dependent transcriptional termination and intrinsic termination (PubMed:31020314). Domain AR2 interacts with a large number of other proteins and may serve as a platform to recruit these factors for transcriptional regulation (PubMed:31127279). Involved in phage lambda N-mediated transcriptional antitermination. Also important for coordinating the cellular responses to DNA damage by coupling the processes of nucleotide excision repair and translesion synthesis to transcription. Monomer. Binds directly to the core enzyme of the DNA-dependent RNA polymerase (RNAP) (PubMed:6263495, PubMed:1856861). Interacts with nascent RNA (PubMed:7536848). Interacts with the termination Rho factor (PubMed:6096352). Interacts with the phage lambda N protein (PubMed:6154941). Interacts with SuhB via the AR2 domain, crystallizes as a 2:1 SuhB:NusA heterotrimer. The rRNA transcription and antitermination complex (rrnTAC) consists of RNAP, NusA, NusB, NusE (rpsJ), NusG, SubB, ribosomal protein S4, DNA and precursor rRNA; S4 is more flexible than other subunits (PubMed:31020314, PubMed:31127279). NusG and the alpha-CTD of RNAP interact with the AR2 domain (PubMed:31127279). (Microbial infection) Interacts (via N-terminus and AR2 domain) with Escherichia phage lambda antitermination protein Q; this interaction (AR2 domain) releases the autoinhibition of NusA. Colocalizes with nucleoids. In response to low temperature. Negatively autoregulated. Induced by cold shock (42 to 15 degrees Celsius) (at protein level) (PubMed:8898389). The N-terminal region interacts with RNAP (PubMed:21922055). The central region is composed of 3 RNA binding domains, S1, KH 1 and KH 2. The C-terminal region contains 2 acidic repeats, AR1 and AR2, which bind to protein N from phage lambda during antitermination. AR2 interacts with SuhB and RNAP alpha subunit C-terminal domain (rpoA); AR2 cannot bind to both simultaneously (PubMed:31020314, PubMed:31127279). SuhB, NusG and the alpha-CTD of RNAP all interact with the AR2 domain and can displace the AR2 domain from the SSK domain (S1, KH1 and KH2) of NusA (PubMed:31127279). Mutants are sensitive to DNA-damaging agents. Belongs to the NusA family.