2024-03-28T07:59:41Zhttp://digital.csic.es/dspace-oai/requestoai:digital.csic.es:10261/131652017-07-04T12:50:23Zcom_10261_59com_10261_6col_10261_312
DIGITAL.CSIC
author
Scott, David J.
author
Ferguson, Anna L.
author
Gallegos, María Trinidad
author
Pitt, Melinda
author
Buck, Martin
author
Hoggett, James G.
2009-05-22T10:53:35Z
2009-05-22T10:53:35Z
2000-12-01
Biochemical Journal 352(2): 539-547 (2000)
0264-6021
http://hdl.handle.net/10261/13165
The equilibrium binding and kinetics of assembly of the DNA-dependent RNA polymerase (RNAP) σ(N)-holoenzyme has been investigated using biosynthetically labelled 7-azatryptophyl- (7AW)σ(N). The spectroscopic properties of such 7AW proteins allows their absorbance and fluorescence to be monitored selectively, even in the presence of high concentrations of other tryptophan-containing proteins. The 7AWσ(N) retained its biological activity in stimulating transcription from σ(N)-specific promoters, and in in vitro gel electrophoresis assays of binding to core RNAP from Escherichia coli. Furthermore, five Trp --> Ala single mutants of σ(N) were shown to support growth under conditions of nitrogen limitation, and showed comparable efficiency in activating the σ(N)-dependent nifH promoter in vivo, indicating that none of the tryptophan residues were essential for activity. The equilibrium binding of 7AWσ(N) to core RNAP was examined by analytical ultracentrifugation. In sedimentation equilibrium experiments, absorbance data at 315 nm (which reports selectively on the distribution of free and bound 7AWσ(N)) established that a 1:1 complex was formed, with a dissociation constant lower than 2 μM. The kinetics of the interaction between 7AWσ(N) and core RNAP was investigated using stopped-flow spectrofluorimetry. A biphasic decrease in fluorescence intensity was observed when samples were excited at 280 nm, whereas only the slower of the two phases was observed at 315 nm. The kinetic data were analysed in terms of a mechanism in which a fast bimolecular association of σ(N) with core RNAP is followed by a relatively slow isomerization step. The consequences of these findings on the competition between σ(N) and the major sigma factor, σ(70), in Escherichia coli are discussed.
eng
openAccess
Analytical ultracentrifugation
Protein-protein interactions
Transcription
Tryptophan analogues
Interaction of sigma factor σ(N) with Escherichia coli RNA polymerase core enzyme
artículo
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URL
https://digital.csic.es/bitstream/10261/13165/1/Scott_2000.pdf
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Scott_2000.pdf.txt