NusA modulates intragenic termination by different pathways.
In bacteria, conditions that uncouple translation from transcription activate intragenic terminators located within cistrons. We analyzed the function of NusA in intragenic termination, making use of two tandem terminators located within the hisG cistron, GTTE1 and GTTE2. GTTE2 is a canonical Rho site, capable to terminate with Rho alone in vitro. By contrast, GTTE1 is a suboptimal terminator, featuring a boxA element and requiring a functional NusB to terminate efficiently in vivo. We found that a functional NusA is necessary for efficient termination events to occur at both GTTE1 and 2. To enhance termination at GTTE1 in conditions in which the transcript is free of ribosomes, NusA acts at the same step as NusB and NusE/S10. In the presence of concomitant translation, termination at GTTE1 is dependent on the relative position of the translation stop codon and boxA. If translation stops upstream of boxA, NusA acts at the same step as NusB enhance termination. Ribosomes terminating translation at boxA influence termination at GTTE1. Interactions of NusA and/or NusB with ribosomal components, including NusE/S10, might facilitate termination. Differently from what observed at GTTE1, the NusA-stimulated pausing seems to be sufficient for the occurrence of complete termination events at GTTE2. A functional NusA is also necessary to prevent premature termination of normally translated transcripts. Our data support the hypothesis that NusA may program a fraction of the RNA polymerase to terminate transcription upon interactions with specific sites on the nascent mRNA and either other Nuses or ribosomes.
Carlomagno
M Stella
MS
Dipartimento di Biologia e Patologia Cellulare e Molecolare L. Califano, Università degli Studi di Napoli Federico II, Via S. Pansini 5, 80131 Naples, Italy. carloma@unina.it
Nappo
Annagiulia
A
D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D006639:Histidine / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D009154:Mutation; D009876:Operon / Q000235:genetics; D010445:Peptide Elongation Factors / Q000235:genetics / Q000502:physiology*; D014176:Protein Biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013728:Terminator Regions, Genetic / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics; D035602:Transcriptional Elongation Factors
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C106638:HisG protein, bacteria; D009004:Monosaccharide Transport Proteins; C074952:NusB protein, E coli; D010445:Peptide Elongation Factors; D012333:RNA, Messenger; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C068727:nusA protein, E coli; D006639:Histidine; D012321:DNA-Directed RNA Polymerases