Mihara Hisaaki, Hidese Ryota, Yamane Masahiro, Kurihara Tatsuo, Esaki Nobuyoshi
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
Biochem Biophys Res Commun. 2008 Aug 1;372(3):407-11. doi: 10.1016/j.bbrc.2008.05.019. Epub 2008 May 13.
Inactivation of iscS encoding cysteine desulfurase results in a slow growth phenotype associated with the deficiency of iron-sulfur clusters, thiamine, NAD, and tRNA thionucleosides in Escherichia coli. However, the other roles of iscSin vivo are unknown. By using differential screening strategies, we identified 2 pyrimidine salvage enzymes, namely, uridine phosphorylase and cytidine deaminase, which were down-regulated in the iscS mutant. Both enzymes are positively regulated by the cAMP receptor protein (CRP). We also identified a novel protein complex, namely, YeiT-YeiA, whose expression level was decreased in the iscS mutant. The recombinant YeiT-YeiA complex exhibited NADH-dependent dihydropyrimidine dehydrogenase activity, indicating its role in pyrimidine metabolism. The presence of a CRP-binding consensus sequence on the 5'-upstream of the yeiT-YeiA gene suggests its regulation by CRP. These results provide a clue to the possible role of iscS in pyrimidine metabolism by gene regulation.
编码半胱氨酸脱硫酶的iscS失活会导致大肠杆菌中出现与铁硫簇、硫胺素、烟酰胺腺嘌呤二核苷酸（NAD）和tRNA硫代核苷缺乏相关的生长缓慢表型。然而，iscS在体内的其他作用尚不清楚。通过使用差异筛选策略，我们鉴定出2种嘧啶补救酶，即尿苷磷酸化酶和胞苷脱氨酶，它们在iscS突变体中表达下调。这两种酶均受环磷酸腺苷受体蛋白（CRP）的正调控。我们还鉴定出一种新型蛋白复合物，即YeiT-YeiA，其在iscS突变体中的表达水平降低。重组的YeiT-YeiA复合物表现出依赖烟酰胺腺嘌呤二核苷酸（NADH）的二氢嘧啶脱氢酶活性，表明其在嘧啶代谢中的作用。在yeiT-YeiA基因5'上游存在CRP结合共有序列，提示其受CRP调控。这些结果为iscS通过基因调控在嘧啶代谢中可能发挥的作用提供了线索。
