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Description (originally from EcoCyc[1][2]) EIIAsc

Comments (originally from EcoCyc[1][2]) AscF, the Arbutin/Salicin/Cellobiose PTS permease, belongs to the functional superfamily of the phosphoenolpyruvate (PEP)-dependent, sugar transporting phosphotransferase system (PTS). The PTS transports and simultaneously phosphorylates its sugar substrates in a process called group translocation. AscF takes up exogenous β-glucosides, releasing the phosphate esters into the cell cytoplasm in preparation for hydrolysis and metabolism, primarily via glycolysis [3][4]. Crypticity of this and other E. coli β-glucoside metabolic operons presumably serves as a protective device against toxic β-glucosides found in nature. The asc operon contains the ascF gene encoding the Enzyme IIAsc and the ascB gene encoding a phospho-β-glucosidase that hydrolyzes the aglycone from the glycoside phosphate ester. The monocistronic ascG gene, encoding the repressor of the ascFB operon, and the ascFB operon are transcribed from divergent promoters. AscF and AscB are paralogues of BglF and BglA, respectively. AscG is paralogous to GalR. The bgl and asc operons are estimated to have arisen by operon duplication about 3x108 years ago.


  1. 1.0 1.1 EcoCyc (release 10.6; 2007) Keseler, IM et al. (2005) Nucleic Acids Res. 33(Database issue):D334-7
  2. 2.0 2.1 EcoCyc (release 11.1; 2007) Keseler, IM et al. (2005) Nucleic Acids Res. 33(Database issue):D334-7
  3. Postma, PW et al. (1993) Phosphoenolpyruvate:carbohydrate phosphotransferase systems of bacteria. Microbiol. Rev. 57 543-94 PubMed
  4. Hall, BG & Xu, L (1992) Nucleotide sequence, function, activation, and evolution of the cryptic asc operon of Escherichia coli K12. Mol. Biol. Evol. 9 688-706 PubMed

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