Ogawa W, Kayahara T, Tsuda M, Mizushima T, Tsuchiya T
Department of Microbiology, Faculty of Pharmaceutical Science, Okayama University, Tsushima.
J Biochem. 1997 Dec;122(6):1241-5. doi: 10.1093/oxfordjournals.jbchem.a021887.
L-Serine as well as L-valine inhibits the growth of Escherichia coli cells, and L-isoleucine releases this growth inhibition. We isolated an E. coli mutant (designated as WAT9) that was able to grow on lactate (or glucose) as a carbon source even in the presence of L-serine, the parent not being able to. Cells of WAT9 were not able to grow on L-serine as a carbon source even if L-isoleucine was present in the culture medium, while the parental cells grew. This mutant was shown to lack the principal L-serine transporter in E. coli, the Na+/ serine symporter. This mutant is useful for analysis of the role(s) of the Na+/serine symporter in cell physiology and as a host for the cloning of L-serine transporter gene(s). In fact, we cloned a gene encoding a serine transporter from chromosomal DNA of E. coli using WAT9 as the host. The gene enabled the mutant cells to grow on L-serine. Transport activity for L-serine was restored in the mutant cells harboring a plasmid carrying the gene. We partially sequenced the gene and found that it was the tdcC gene. We showed that TdcC is an H+/serine symporter.
L-丝氨酸以及L-缬氨酸会抑制大肠杆菌细胞的生长，而L-异亮氨酸可解除这种生长抑制。我们分离出了一种大肠杆菌突变体（命名为WAT9），它即使在存在L-丝氨酸的情况下也能够以乳酸（或葡萄糖）作为碳源生长，而其亲本则不能。即使培养基中存在L-异亮氨酸，WAT9细胞也无法以L-丝氨酸作为碳源生长，而亲本细胞却可以。已证明该突变体缺乏大肠杆菌中的主要L-丝氨酸转运体，即Na⁺/丝氨酸同向转运体。该突变体对于分析Na⁺/丝氨酸同向转运体在细胞生理学中的作用以及作为克隆L-丝氨酸转运体基因的宿主很有用。实际上，我们以WAT9作为宿主，从大肠杆菌的染色体DNA中克隆了一个编码丝氨酸转运体的基因。该基因使突变体细胞能够在L-丝氨酸上生长。在携带该基因的质粒的突变体细胞中，L-丝氨酸的转运活性得以恢复。我们对该基因进行了部分测序，发现它是tdcC基因。我们证明TdcC是一种H⁺/丝氨酸同向转运体。
