title: Two nucleoside transporters in Lactococcus lactis with different substrate specificities.
abstract: In an alternative to biosynthesis of nucleotides, most organisms are capable of exploiting exogenous nucleotide sources. In order to do so, the nucleotide precursors must pass the membrane, which requires the presence of transporters. Normally, phosphorylated compounds are not subject to transport, and the utilization of nucleotides is dependent on exogenous phosphatases. The composition of transporters with specificity for purine and pyrimidine nucleosides and nucleobases is subject to variation. The ability of Lactococcus lactis to transport different nucleosides across the cell membrane was characterized at both genetic and physiological level, using mutagenesis and by measuring the growth and uptake of nucleosides in the different mutants supplemented with different nucleosides. Two high affinity transporters were identified: BmpA-NupABC was shown to be an ABC transporter with the ability to actively transport all common nucleosides, whereas UriP was shown to be responsible for the uptake of only uridine and deoxyuridine. Interestingly, the four genes encoding the ABC transporter were found at different positions on the chromosome. The bmpA gene was separated from the nupABC operon by 60 kb. Moreover, bmpA was subject to regulation by purine availability, whereas the nupABC operon was constitutively expressed.
authors.affiliation: Center for Systems Microbiology, DTU-Systems Biology, Building 301, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark.
authors.forename: Jan
authors.initials: J
authors.lastname: Martinussen
authors.affiliation: Center for Systems Microbiology, DTU-Systems Biology, Building 301, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark.
authors.forename: Claus
authors.initials: C
authors.lastname: Sørensen
authors.affiliation: Center for Systems Microbiology, DTU-Systems Biology, Building 301, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark.
authors.forename: Christian Bille
authors.initials: CB
authors.lastname: Jendresen
authors.affiliation: Center for Systems Microbiology, DTU-Systems Biology, Building 301, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark.
authors.forename: Mogens
authors.initials: M
authors.lastname: Kilstrup
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D005798:Genes, Bacterial; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism; D016296:Mutagenesis; D009154:Mutation; D033703:Nucleoside Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009705:Nucleosides / Q000096:biosynthesis*; D009876:Operon; D013379:Substrate Specificity; D014529:Uridine / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D033703:Nucleoside Transport Proteins; D009705:Nucleosides; D014529:Uridine