<p>This entry describes NusA, or N utilisation substance protein A, a bacterial transcription termination factor. It binds to RNA polymerase alpha subunit and promotes termination at certain RNA hairpin structures. It is named for the interaction in <taxon tax_id="562">Escherichia coli</taxon> of <taxon tax_id="10710">Bacteriophage lambda</taxon> antitermination protein N with the N-utilisation substance, consisting of NusA, NusB, NusE (ribosomal protein S10), and NusG [<cite idref="PUB00013514"/>]. This entry represents a region of NusA shared by all bacterial forms, and includes the S1 (<db_xref db="INTERPRO" dbkey="IPR003029"/>) and KH RNA binding domains. Proteobacterial forms have an additional C-terminal region, not included in this entry, with two repeats of 50-residue domain rich in acidic amino acids.</p>