Transcription-frequency-dependent modulation of an attenuator in a ribosomal protein-RNA polymerase operon requires an upstream site.
Although the attenuator located between the ribosomal protein and RNA polymerase gene domains of the Escherichia coli rplKAJLrpoBC operon has a maximum termination efficiency of 80%, the level of termination is diminished with decreasing transcription frequency. In this report, the use of transcriptional fusions to further investigate the mechanism of transcription-frequency-dependent regulation is described. The termination efficiency of two other weak terminators was assayed over a wide range of transcription frequencies programmed by different strength promoters. The results indicated that a decrease in termination efficiency with decreasing transcription frequency is not an inherent property of weak terminators. Deletion of the 165 bp segment located 439-274 bp upstream of the attenuator abrogated the difference in termination efficiency normally seen between high and low levels of transcription. This suggests that a cis-acting site located in this upstream region is necessary for transcription-frequency-dependent modulation of the attenuator's function. However, this site apparently works only in combination with the attenuator, since it did not cause transcription-frequency-dependent modulation when placed upstream of two other weak terminators. Analysis of the readthrough frequencies of single or tandem copies of the attenuator indicated that the transcription complexes which pass through the attenuator have not been converted to termination-resistant complexes in a manner analogous to the N-mediated antitermination system of lambda. Finally, an examination of termination efficiency in three nusA mutants suggested that although NusA increases readthrough at the attenuator it is not directly involved in transcription-frequency-dependent modulation.
Steward
Keith L
KL
Pierre
Rebecca St
RS
Department of Microbiology and Immunology, Faculty of Medicine, University of Western Ontario, London, Ontario, Canada N6A 5C1.
Linn
Thomas
T
Department of Microbiology and Immunology, Faculty of Medicine, University of Western Ontario, London, Ontario, Canada N6A 5C1.
D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D004274:DNA, Recombinant / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D007763:Lac Operon / Q000235:genetics; D009876:Operon / Q000235:genetics*; D010445:Peptide Elongation Factors; D011401:Promoter Regions, Genetic / Q000235:genetics; D012269:Ribosomal Proteins / Q000235:genetics*; D017384:Sequence Deletion; 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; D004274:DNA, Recombinant; D029968:Escherichia coli Proteins; D010445:Peptide Elongation Factors; D012269:Ribosomal Proteins; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; C068727:nusA protein, E coli; D012321:DNA-Directed RNA Polymerases