Scotti C, Valbuzzi A, Perego M, Galizzi A, Albertini A M
Dipartimento di Genetica e Microbiologia, A. Buzzati Traverso, Università degli Studi di Pavia, Italy.
Microbiology (Reading). 1996 Nov;142 ( Pt 11):2995-3004. doi: 10.1099/13500872-142-11-2995.
We have cloned and sequenced the nrd (nucleotide reductase) locus of Bacillus subtilis. The locus seems to be organized in an operon comprising four ORFs. The first three encode polypeptides highly similar to the product of the coding sequences characterizing the nrdEF operons of Enterobacteriaceae. The sequencing of the conditional lethal mutation ts-A13, localized in the nrdE cistron, and the lethality of insertional mutations targeted in the internal region of nrdE and nrdF, demonstrated the essential role of this locus. The fourth ORF, ymaB, part of the putative operon, which is not similar to any known protein, is also essential. The regulation of expression of the operon, monitored by lacZ transcriptional fusions, is similar to the regulation of the functionally relevant nrdAB operon of Escherichia coli. The operon was induced by thymidine starvation and its expression was directly or indirectly affected by RecA function. Genetic and functional analysis strongly indicates that in B. subtilis the class I ribonucleotide reductase encoded by this nrd operon is evolutionarily distant from the homologous class I enzyme of Enterobacteria.
我们已经克隆并测序了枯草芽孢杆菌的nrd（核苷酸还原酶）基因座。该基因座似乎以一个包含四个开放阅读框（ORF）的操纵子形式组织。前三个编码的多肽与肠杆菌科nrdEF操纵子编码序列的产物高度相似。定位在nrdE顺反子中的条件致死突变ts - A13的测序，以及针对nrdE和nrdF内部区域的插入突变的致死性，证明了该基因座的重要作用。第四个开放阅读框ymaB是假定操纵子的一部分，与任何已知蛋白质都不相似，也是必不可少的。通过lacZ转录融合监测该操纵子的表达调控，与大肠杆菌功能相关的nrdAB操纵子的调控相似。该操纵子由胸苷饥饿诱导，其表达直接或间接受RecA功能的影响。遗传和功能分析有力地表明，在枯草芽孢杆菌中，由这个nrd操纵子编码的I类核糖核苷酸还原酶在进化上与肠杆菌的同源I类酶相距甚远。
