Greener T, Govezensky D, Zamir A
Biochemistry Department, Weizmann Institute of Science, Rehovot, Israel.
EMBO J. 1993 Mar;12(3):889-96. doi: 10.1002/j.1460-2075.1993.tb05729.x.
When present on a multicopy plasmid, a newly discovered gene (sugE) mapping to 94 min on the Escherichia coli chromosome, suppresses a groEL mutation and mimics the effects of groE overexpression. A groEL mutant of E.coli, transformed with the Klebsiella pneumoniae nif gene cluster, failed to accumulate nitrogenase components [Govezensky et al. (1991) J. Bacteriol., 173, 6339-6346]. Transformation with sugE reversed the mutant phenotype. In wild type K.pneumoniae, transformation with sugE accelerated the rate of nitrogenase biogenesis after nif derepression. In E.coli, transformation with sugE enabled bacteriophage T4 growth in a groEL mutant. A continuous 178 codon open reading frame (ORF) in sugE encloses another, in-frame, 105 codon ORF similar to a predicted ORF in Proteus vulgaris. In vivo products of both sugE ORFs were observed in transformants expressing the gene from a T7 promoter. In non-transformed cells, a typical sigma 70-dependent promoter found upstream of the larger ORF directs sugE transcription during growth at 30 degrees C. At elevated temperatures or in stationary phase cells, another promoter, found within the coding sequence upstream of the smaller ORF, is activated independently of sigma 32. The results suggest that sugE encodes a chaperonin-related system whose composition might vary with temperature and growth phase.
当一个新发现的基因（sugE）存在于多拷贝质粒上时，它定位于大肠杆菌染色体的94分钟处，可抑制groEL突变并模拟groE过表达的效果。用肺炎克雷伯菌nif基因簇转化的大肠杆菌groEL突变体无法积累固氮酶成分[戈韦曾斯基等人（1991年）《细菌学杂志》，173，6339 - 6346]。用sugE转化可逆转突变体表型。在野生型肺炎克雷伯菌中，用sugE转化可加快nif去阻遏后固氮酶生物合成的速率。在大肠杆菌中，用sugE转化可使噬菌体T4在groEL突变体中生长。sugE中有一个连续的178个密码子的开放阅读框（ORF），其中包含另一个符合读框的105个密码子的ORF，类似于普通变形杆菌中一个预测的ORF。在从T7启动子表达该基因的转化体中观察到了sugE两个ORF的体内产物。在未转化的细胞中，在较大ORF上游发现的一个典型的依赖sigma 70的启动子在30℃生长期间指导sugE转录。在高温或稳定期细胞中，在较小ORF上游编码序列内发现的另一个启动子独立于sigma 32被激活。结果表明，sugE编码一个与伴侣蛋白相关的系统，其组成可能随温度和生长阶段而变化。
