PathBank

Pathway Description

Operon: Cytosine Transport

Escherichia coli

Category:

Metabolite Pathway

Sub-Category:

Signaling

Created: 2015-10-26

Last Updated: 2025-01-24

The codBA operon in E. coli contains two genes which encode proteins involved in cytosine entry into the cell, as well as its deamination. The operon can be activated by the bining of nitrogen assimilation regulatory protein Nac, which activates transcription at the promoter in the case of low nitrogen levels in the cell. With this operon activated, cytosine can be broken down into the nitrogen source, and can even be the sole nitrogen source if necessary. The operon can also be deactivated by the binding of the PurR transcriptional repressor to the promoter. This repressor is activated by a purine such as guanine, or its derivatives such as hypoxanthine. The first gene in the operon, codB, encodes cytosine permease, an enzyme that is necessary for cytosine to be able to enter the cell. The second gene, codA, encodes cytosine deaminase, an enzyme that catalyzes the deamination of cytosine into uracil, with the addition of a water molecule.

References

Operon: Cytosine Transport References

Danielsen S, Kilstrup M, Barilla K, Jochimsen B, Neuhard J: Characterization of the Escherichia coli codBA operon encoding cytosine permease and cytosine deaminase. Mol Microbiol. 1992 May;6(10):1335-44.

Pubmed: 1640834

Qi F, Turnbough CL Jr: Regulation of codBA operon expression in Escherichia coli by UTP-dependent reiterative transcription and UTP-sensitive transcriptional start site switching. J Mol Biol. 1995 Dec 8;254(4):552-65. doi: 10.1006/jmbi.1995.0638.

Pubmed: 7500333

Muse WB, Rosario CJ, Bender RA: Nitrogen regulation of the codBA (cytosine deaminase) operon from Escherichia coli by the nitrogen assimilation control protein, NAC. J Bacteriol. 2003 May;185(9):2920-6. doi: 10.1128/jb.185.9.2920-2926.2003.

Pubmed: 12700271

Andersen L, Kilstrup M, Neuhard J: Pyrimidine, purine and nitrogen control of cytosine deaminase synthesis in Escherichia coli K 12. Involvement of the glnLG and purR genes in the regulation of codA expression. Arch Microbiol. 1989;152(2):115-8.

Pubmed: 2673119

Pubmed: 1640834

Blattner FR, Plunkett G 3rd, Bloch CA, Perna NT, Burland V, Riley M, Collado-Vides J, Glasner JD, Rode CK, Mayhew GF, Gregor J, Davis NW, Kirkpatrick HA, Goeden MA, Rose DJ, Mau B, Shao Y: The complete genome sequence of Escherichia coli K-12. Science. 1997 Sep 5;277(5331):1453-62. doi: 10.1126/science.277.5331.1453.

Pubmed: 9278503

Hayashi K, Morooka N, Yamamoto Y, Fujita K, Isono K, Choi S, Ohtsubo E, Baba T, Wanner BL, Mori H, Horiuchi T: Highly accurate genome sequences of Escherichia coli K-12 strains MG1655 and W3110. Mol Syst Biol. 2006;2:2006.0007. doi: 10.1038/msb4100049. Epub 2006 Feb 21.

Pubmed: 16738553

Austin EA, Huber BE: A first step in the development of gene therapy for colorectal carcinoma: cloning, sequencing, and expression of Escherichia coli cytosine deaminase. Mol Pharmacol. 1993 Mar;43(3):380-7.

Pubmed: 8450832

Muse WB, Bender RA: The nac (nitrogen assimilation control) gene from Escherichia coli. J Bacteriol. 1998 Mar;180(5):1166-73.

Pubmed: 9495755

Itoh T, Aiba H, Baba T, Hayashi K, Inada T, Isono K, Kasai H, Kimura S, Kitakawa M, Kitagawa M, Makino K, Miki T, Mizobuchi K, Mori H, Mori T, Motomura K, Nakade S, Nakamura Y, Nashimoto H, Nishio Y, Oshima T, Saito N, Sampei G, Seki Y, Horiuchi T, et al.: A 460-kb DNA sequence of the Escherichia coli K-12 genome corresponding to the 40.1-50.0 min region on the linkage map. DNA Res. 1996 Dec 31;3(6):379-92. doi: 10.1093/dnares/3.6.379.

Pubmed: 9097040

Rolfes RJ, Zalkin H: Escherichia coli gene purR encoding a repressor protein for purine nucleotide synthesis. Cloning, nucleotide sequence, and interaction with the purF operator. J Biol Chem. 1988 Dec 25;263(36):19653-61.

Pubmed: 3058704

Meng LM, Kilstrup M, Nygaard P: Autoregulation of PurR repressor synthesis and involvement of purR in the regulation of purB, purC, purL, purMN and guaBA expression in Escherichia coli. Eur J Biochem. 1990 Jan 26;187(2):373-9. doi: 10.1111/j.1432-1033.1990.tb15314.x.

Pubmed: 2404765

Aiba H, Baba T, Hayashi K, Inada T, Isono K, Itoh T, Kasai H, Kashimoto K, Kimura S, Kitakawa M, Kitagawa M, Makino K, Miki T, Mizobuchi K, Mori H, Mori T, Motomura K, Nakade S, Nakamura Y, Nashimoto H, Nishio Y, Oshima T, Saito N, Sampei G, Horiuchi T, et al.: A 570-kb DNA sequence of the Escherichia coli K-12 genome corresponding to the 28.0-40.1 min region on the linkage map. DNA Res. 1996 Dec 31;3(6):363-77. doi: 10.1093/dnares/3.6.363.

Pubmed: 9097039

Highlighted elements will appear in red.

Highlight Compounds

	Fe2+
	Hypoxanthine
	Nitrogen

Highlight Proteins

	Cytosine deaminase
	Cytosine permease
	Nitrogen assimilation regulatory protein nac
	purR transcriptional repressor

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