title: Structure of a Mycobacterium tuberculosis NusA-RNA complex.
abstract: NusA is a key regulator of bacterial transcriptional elongation, pausing, termination and antitermination, yet relatively little is known about the molecular basis of its activity in these fundamental processes. In Mycobacterium tuberculosis, NusA has been shown to bind with high affinity and specificity to BoxB-BoxA-BoxC antitermination sequences within the leader region of the single ribosomal RNA (rRNA) operon. We have determined high-resolution X-ray structures of a complex of NusA with two short oligo-ribonucleotides derived from the BoxC stem-loop motif and have characterised the interaction of NusA with a variety of RNAs derived from the antitermination region. These structures reveal the RNA bound in an extended conformation to a large interacting surface on both KH domains. Combining structural data with observed spectral and calorimetric changes, we now show that NusA binding destabilises secondary structure within rRNA antitermination sequences and propose a model where NusA functions as a chaperone for nascently forming RNA structures.
authors.affiliation: Division of Protein Structure, National Institute for Medical Research, London, UK.
authors.forename: Barbara
authors.initials: B
authors.lastname: Beuth
authors.forename: Simon
authors.initials: S
authors.lastname: Pennell
authors.forename: Kristine B
authors.initials: KB
authors.lastname: Arnvig
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Martin
authors.forename: Ian A
authors.initials: IA
authors.lastname: Taylor
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D001483:Base Sequence; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000235:genetics*; D009690:Nucleic Acid Conformation; D010445:Peptide Elongation Factors / Q000737:chemistry*; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000737:chemistry; D012335:RNA, Ribosomal / Q000737:chemistry*; D016601:RNA-Binding Proteins / Q000737:chemistry*; D014157:Transcription Factors / Q000737:chemistry*; D035602:Transcriptional Elongation Factors
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D010445:Peptide Elongation Factors; D012329:RNA, Bacterial; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C068727:nusA protein, E coli