RT Journal Article SR Electronic(1) A1 Danielsen, Steffen A1 Boyd, Dana A1 Neuhard, JanYR 1995 T1 Membrane topology analysis of the Escherichia coli cytosine permease JF Microbiology, VO 141 IS 11 SP 2905 OP 2913 DO https://doi.org/10.1099/13500872-141-11-2905 PB Microbiology Society, SN 1465-2080, AB 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., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/13500872-141-11-2905