10-Ntr_promoters

10-Ntr_promoters - Regulation of nitrogen assimilation...

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Regulation of nitrogen assimilation (ntr) genes of E. coli Promoters-recognised by RNA polymerase containing σ 54 TTGGCACA-N4-TTGCT Very highly conserved GG and GC at -24 and -12 the spacer is always 10 bp E σ 54 binds stably to the promoters, but cannot form the open complex Formation of the open complex requires an activator. For E. coli ntr genes, the activator is a phosphoprotein known as NRI~P NRI~P binds to enhancer and silencer sequences far from promoter. Activation requires a DNA loop. Silencing antagonises loop formation. Factors that affect loop formation regulate transcription, as do factors the influence the phosphorylation of NRI.
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Activation of an Ntr promoter promoter enhancer (two adjacent sites for dimer to bind) NRI~P E σ 54 DNA looping required for interaction of polymerase with activator. ATP cleavage by NRI~P required for open complex formation. DNA looping may be due to intrinsic sequence, or due to a protein that bends DNA A repressor may act by bending the DNA in an unfavorable way.
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10-Ntr_promoters - Regulation of nitrogen assimilation...

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