1] Arc System (Aerobic respiration control)

Regulatory System :

Three systems for regulation of gene expression by Oxygen or Nitrate in E.coli out of three, two of these are responsible by Oxygen and 3rd regulated by Nitrate.

1] Arc System (Aerobic respiration control) :

This system represses the transcription of aerobic genes and stimulates the transcription of genes for cytochrome d oxidation.

Arc system consists of HK, Arc B and partner response regulator, Arc A.

Phosphorylated Arc A is responsible for -

i) Anaerobic repression of the genes for Citric acid cycle enzymes (succinate dehydrogenase), Glyoxylate cycle enzyme (oxoglutarate dehydrogenase), Pyruvate drhydrogenase, Fatty acid oxidation enzymes, Cytochrome O oxidase.

ii) Induction of the genes for - Cytochrome d oxidase and Cobalamin synthesis.

Arc B protein monitors the level of the oxygen indirectly and that when oxygen levels are low, the Arc B protein autophosphorylates using ATP and then transfers the phosphoryl group to Arc B.

The phosphorylated Arc A-p repress the aerobically expressed enzymes and induces cytochrome d oxidase.

Arc A-p also activates the genes for (S.typhi) Cobalamin synthesis.

Arc A respond to CpxA which is membrane bound sensor protein necessory  for the synthesis of F-pilus and other sex factor functions.