Okumura Noriko, Masamoto Kazumori, Wada Hajime
Biological Laboratory, Faculty of Education, Kumamoto University, Kurokami, Kumamoto 860, Japan.
Department of Biology, Faculty of Science, Kyushu University, Fukuoka 810, Japan.
Microbiology (Reading). 1997 Sep;143 ( Pt 9):2883-2890. doi: 10.1099/00221287-143-9-2883.
The gene homologous to glutathione synthetase of Escherichia coli was inactivated in the cyanobacterium Synechococcus sp. PCC 7942. The region of genomic DNA including the mutation site was isolated from the mutant by plasmid rescue and the native gene of the wild-type was cloned from a genomic DNA library of the wild-type using the flanking DNA as a probe. The wild-type gene, designated gshB, encodes a polypeptide of 323 amino acids with a molecular mass of 35 kDa. The deduced amino acid sequence resembles glutathione synthetases of bacteria, but not those of higher organisms. When gshB was overexpressed in E. coli, glutathione synthetase activity was increased markedly in the E. coli extract. In addition, the Synechococcus sp. PCC 7942 gshB mutants had lost their ability to synthesize glutathione. These findings demonstrate that the gshB gene of Synechococcus sp. PCC 7942 is a structural gene for glutathione synthetase and is involved in the biosynthesis of glutathione.
在蓝藻聚球藻属（Synechococcus sp.）PCC 7942中，与大肠杆菌谷胱甘肽合成酶同源的基因被灭活。通过质粒拯救从突变体中分离出包含突变位点的基因组DNA区域，并以侧翼DNA为探针，从野生型的基因组DNA文库中克隆出野生型的天然基因。该野生型基因命名为gshB，编码一个由323个氨基酸组成、分子量为35 kDa的多肽。推导的氨基酸序列与细菌的谷胱甘肽合成酶相似，但与高等生物的不同。当gshB在大肠杆菌中过表达时，大肠杆菌提取物中的谷胱甘肽合成酶活性显著增加。此外，聚球藻属PCC 7942 gshB突变体失去了合成谷胱甘肽的能力。这些发现表明，聚球藻属PCC 7942的gshB基因是谷胱甘肽合成酶的结构基因，参与谷胱甘肽的生物合成。
