Center for Systems Microbiology, DTU-Systems Biology, Building 301, Technical University of Denmark, DK-2800 Kgs Lyngby, Denmark.
Microbiology (Reading). 2010 Oct;156(Pt 10):3148-3157. doi: 10.1099/mic.0.039818-0. Epub 2010 Jul 1.
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.
在核苷酸的生物合成替代途径中，大多数生物体能够利用外源核苷酸源。为了做到这一点，核苷酸前体必须穿过细胞膜，这需要转运体的存在。通常，磷酸化化合物不受运输的影响，并且核苷酸的利用依赖于外源磷酸酶。具有嘌呤和嘧啶核苷和碱基特异性的转运体的组成是可变的。通过诱变和测量不同突变体在补充不同核苷时的生长和摄取来研究乳球菌的不同核苷穿过细胞膜的运输能力，在遗传和生理水平上进行了表征。鉴定出两种高亲和力转运体：BmpA-NupABC 被证明是一种能够主动转运所有常见核苷的 ABC 转运体，而 UriP 则负责摄取尿嘧啶和脱氧尿嘧啶。有趣的是，编码 ABC 转运体的四个基因位于染色体的不同位置。bmpA 基因与 nupABC 操纵子之间相隔 60kb。此外，bmpA 受嘌呤可用性的调节，而 nupABC 操纵子则组成型表达。
