title: Nus transcription elongation factors and RNase III modulate small ribosome subunit biogenesis in Escherichia coli.
abstract: Escherichia coli NusA and NusB proteins bind specific sites, such as those in the leader and spacer sequences that flank the 16S region of the ribosomal RNA transcript, forming a complex with RNA polymerase that suppresses Rho-dependent transcription termination. Although antitermination has long been the accepted role for Nus factors in rRNA synthesis, we propose that another major role for the Nus-modified transcription complex in rrn operons is as an RNA chaperone insuring co-ordination of 16S rRNA folding and RNase III processing that results in production of proper 30S ribosome subunits. This contrarian proposal is based on our studies of nusA and nusB cold-sensitive mutations that have altered translation and at low temperature accumulate 30S subunit precursors. Both phenotypes are suppressed by deletion of RNase III. We argue that these results are consistent with the idea that the nus mutations cause altered rRNA folding that leads to abnormal 30S subunits and slow translation. According to this idea, functional Nus proteins stabilize an RNA loop between their binding sites in the 5' RNA leader and on the transcribing RNA polymerase, providing a topological constraint on the RNA that aids normal rRNA folding and processing.
authors.affiliation: Frederick National Laboratory for Cancer Research, Basic Research Program, SAIC-Frederick, Inc., Frederick, MD 21702, USA.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Bubunenko
authors.forename: Donald L
authors.initials: DL
authors.lastname: Court
authors.forename: Abdalla
authors.initials: A
authors.lastname: Al Refaii
authors.forename: Shivalika
authors.initials: S
authors.lastname: Saxena
authors.forename: Alexey
authors.initials: A
authors.lastname: Korepanov
authors.forename: David I
authors.initials: DI
authors.lastname: Friedman
authors.forename: Max E
authors.initials: ME
authors.lastname: Gottesman
authors.forename: Jean-Hervé
authors.initials: JH
authors.lastname: Alix
mesh_terms: D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D008954:Models, Biological; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D009690:Nucleic Acid Conformation; D010445:Peptide Elongation Factors / Q000235:genetics / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000096:biosynthesis*; D043244:Ribonuclease III / Q000378:metabolism*; D054679:Ribosome Subunits, Small / Q000378:metabolism; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D035602:Transcriptional Elongation Factors
chemical_list: D029968:Escherichia coli Proteins; D050505:Mutant Proteins; C074952:NusB protein, E coli; D010445:Peptide Elongation Factors; D012336:RNA, Ribosomal, 16S; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C068727:nusA protein, E coli; D043244:Ribonuclease III