f Membrane topology analysis of the Escherichia coli cytosine permease
- Authors: Steffen Danielsen, Dana Boyd, Jan Neuhard3
- Author for correspondence: Jan Neuhard. Tel: +45 35 322007. Fax: +45 35 322040. e-mail: firstname.lastname@example.org
- Microbiology, November 1995 141: 2905-2913, doi: 10.1099/13500872-141-11-2905
- Subject: Genetics And Molecular Biology
- Published Online:
Summary: The Escherichia coli codBA operon encodes cytosine permease (CodB) and cytosine deaminase (CodA). CodB mediates uptake of exogenously supplied cytosine, and CodA catalyses the hydrolytic deamination of cytosine to uracil and ammonia. The hydropathic profile of CodB indicates that it is an integral cytoplasmic membrane protein possessing several transmembrane-spanning domains. The membrane topology of CodB was investigated by using gene fusions containing varying lengths of the amino-terminus of CodB fused to either alkaline phosphatase (AP) or β-galactosidase (BG). The AP activities expressed by the CodB-AP fusions are consistent with a topological model in which the amino- and the carboxy-termini of CodB are located in the cytoplasm, and in which CodB possesses 12 membrane-spanning segments. The enzyme activities of most of the CodB-BG fusions support the model. However, the results obtained with some of the CodB-BG fusions illustrate the limitations of using BG as a reporter protein in studies of membrane protein topology.
© Society for General Microbiology 1995 | Published by the Microbiology Society
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