CLONING AND EXPRESSION OF THE MEP1 GENE ENCODING AN AMMONIUM TRANSPORTER IN SACCHAROMYCES-CEREVISIAE
CLONING AND EXPRESSION OF THE MEP1 GENE ENCODING AN AMMONIUM TRANSPORTER IN SACCHAROMYCES-CEREVISIAE
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DOI：
10.1002/j.1460-2075.1994.tb06651.x
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发表时间：
1994-08-01
期刊：
影响因子：
11.4
通讯作者：
ANDRE, B
中科院分区：
文献类型：
--
作者：
MARINI, AM;VISSERS, S;ANDRE, B
在酿酒酵母中，铵穿过质膜作为氮源的运输是由至少两个功能不同的运输系统介导的，其各自的编码基因称为MEP1和MEP2。 MEP2 基因的突变影响高亲和力、低容量的铵转运，而 MEP1 基因的突变则破坏低亲和力、高容量的系统。在这项工作中，MEP1 基因已被克隆、测序并分析其表达。预测的氨基酸序列揭示了一种高度疏水性的 54 kDa 蛋白质，具有 10 或 11 个假定的跨膜区域。预测的 Mep1p 蛋白与几种功能未知的细菌蛋白具有高度的序列相似性，特别是枯草芽孢杆菌氮调节 nrgA 基因的产物，以及来自秀丽隐杆线虫的部分 cDNA 序列。 Mep1p 和相关蛋白似乎定义了一个新的跨膜蛋白家族，该家族至少在细菌、真菌和动物中进化上保守。当细胞在低浓度的铵或尿素或脯氨酸等“贫”氮源上生长时，MEP1 基因表达最高。另一方面，当铵浓度较高或培养基中提供其他“良好”氮源（如谷氨酰胺或天冬酰胺）时，它会下调。 Mep1p 的整体特性表明它是铵的转运蛋白。其主要功能似乎是使在氮限制条件下生长的细胞能够掺入生长培养基中浓度相对较低的铵。
In Saccharomyces cerevisiae, the transport of ammonium across the plasma membrane for use as a nitrogen source is mediated by at least two functionally distinct transport systems whose respective encoding genes are called MEP1 and MEP2. Mutations in the MEP2 gene affect high affinity, low capacity ammonium transport while mutations in the MEP1 gene disrupt a lower affinity, higher capacity system. In this work, the MEP1 gene has been cloned and sequenced and its expression analyzed. The predicted amino acid sequence reveals a highly hydrophobic, 54 kDa protein with 10 or 11 putative membrane-spanning regions. The predicted Mep1p protein shares high sequence similarity with several bacterial proteins of unknown function, notably the product of the nitrogen-regulated nrgA gene of Bacillus subtilis, and with that of a partial cDNA sequence derived from Caenorhabditis elegans. The Mep1p and related proteins appear to define a new family of transmembrane proteins evolutionarily conserved in at least bacteria, fungi and animals. The MEP1 gene is most highly expressed when the cells are grown on low concentrations of ammonium or on 'poor' nitrogen sources like urea or proline. It is down-regulated, on the other hand, when the concentration of ammonium is high or when other 'good' nitrogen sources like glutamine or asparagine are supplied in the culture medium. The overall properties of Mep1p indicate that it is a transporter of ammonium. Its main function appears to be to enable cells grown under nitrogen-limiting conditions to incorporate ammonium present at relatively low concentrations in the growth medium.