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Nucleic Acids Research logoLink to Nucleic Acids Research
. 1999 Jun 15;27(12):2478–2486. doi: 10.1093/nar/27.12.2478

Characterisation of holoenzyme lacking sigmaN regions I and II.

W Cannon 1, M Chaney 1, M Buck 1
PMCID: PMC148451  PMID: 10352177

Abstract

The sigma-N (sigmaN) protein associates with bacterial core RNA polymerase to form a holoenzyme that is silent for transcription in the absence of enhancer-binding activator proteins. Here we show that the acidic Region II of sigmaN from Klebsiella pneumoniae is dispensable for polymerase isomerisation and trans-cription under conditions where the inhibited state of the holoenzyme is relieved by removal of sigmaN Region I sequences. Holoenzymes lacking Region I or Regions I+II were equally susceptible to the order of addition-dependent inhibition or stabilisation of DNA binding afforded by in trans Region I sequences. Region I+II-deleted [sigma] formed a holoenzyme with a DNA-binding activity more susceptible to inhibition by non-specific DNA than that lacking Region I. Region II sequences appear more closely associated with formation of a holoenzyme and [sigma] proficient in DNA binding than with changes in holoenzyme conformation needed for unmasking a single-strand DNA-binding activity used for open complex for-mation. Region II may therefore function to optimise DNA interactions for an efficient sigma cycle.

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