In a class of its own — the RNA polymerase sigma factor σ;54N)


  • M. J. Merrick

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    1. AFRC Nitrogen Fixation Laboratory, University of Sussex, Brighton BN1 9RQ, UK.
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Bacteria synthesize a number of different sigma factors which allow the co-ordinate expression of groups of genes owing to the ability of sigma to confer promoter-specific transcription initiation on RNA polymerase. In nearly all cases these sigmas belong to a single family of proteins which appear to be related structurally and functionally to the major Escherichia coli sigma factor, σ;70. A clear exception is the Sigma factor σ;54N), encoded by rpoN, which represents a second family of sigmas that is widely distributed in prokaryotes. Studies of σ;54N) have demonstrated that this sigma is quite distinct both structurally and functionally from the σ;70 family and the mode of transcription initiation which it mediates may have more in common with that found in eukaryotes than that which occurs with σ;70 and its relatives.