Whipp M J, Camakaris H, Pittard A J
Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria, 3052, Australia.
Gene. 1998 Mar 16;209(1-2):185-92. doi: 10.1016/s0378-1119(98)00043-2.
In Escherichia coli K-12, the shiA gene is involved in the uptake of shikimate. This gene has been cloned and its nucleotide sequence determined. The gene is predicted to encode a protein of 438 amino acids and lies adjacent to the amn gene. The hydropathy profile and the amino acid sequence indicate that the ShiA protein is a polytopic membrane protein that shows a homology with members of the major facilitator superfamily of transport proteins. Recombining an inactive form of the cloned gene into the chromosome creates mutants unable to transport shikimate. Introducing a wild-type gene on a multicopy plasmid into a shiA mutant restores the ability to transport shikimate. When this multicopy shiA plasmid is introduced into an aroE strain, this strain is now able to grow with shikimate as the aromatic supplement, consistent with the notion that dehydroshikimate (DHS) accumulated in an aroE strain prevents uptake of shikimate by competition. Expression of the shiA gene does not appear to be regulated by the TyrR protein, a repressor/activator that controls the expression of other genes involved with the biosynthesis or transport of the aromatic amino acids.
在大肠杆菌K-12中，shiA基因参与莽草酸的摄取。该基因已被克隆并测定了其核苷酸序列。预计该基因编码一个由438个氨基酸组成的蛋白质，且位于amn基因附近。亲水性图谱和氨基酸序列表明，ShiA蛋白是一种多跨膜蛋白，与主要协助转运蛋白超家族的成员具有同源性。将克隆基因的无活性形式重组到染色体中会产生无法转运莽草酸的突变体。将携带野生型基因的多拷贝质粒导入shiA突变体可恢复其转运莽草酸的能力。当将这种多拷贝shiA质粒导入aroE菌株时，该菌株现在能够以莽草酸作为芳香族补充物生长，这与aroE菌株中积累的脱氢莽草酸（DHS）通过竞争阻止莽草酸摄取的观点一致。shiA基因的表达似乎不受TyrR蛋白的调控，TyrR蛋白是一种阻遏物/激活剂，可控制参与芳香族氨基酸生物合成或转运的其他基因的表达。
