Chen K S, Saxena P, Walker J R
Department of Microbiology, University of Texas, Austin 78712-1095.
J Bacteriol. 1993 Oct;175(20):6663-70. doi: 10.1128/jb.175.20.6663-6670.1993.
The Escherichia coli dnaX gene encodes both the tau and gamma subunits of DNA polymerase III. This gene is located immediately downstream of the adenine salvage gene apt and upstream of orf12-recR, htpG, and adk. The last three are involved in recombination, heat shock, and nucleotide biosynthesis, respectively. apt, dnaX, and orf12-recR all have separate promoters, and the first two are expressed predominantly from those separate promoters. However, use of an RNase E temperature-sensitive mutant allowed the detection of lesser amounts of polycistronic messengers extending from both the apt and dnaX promoters through htpG. Interestingly, transcription of the weak dnaX promoter is stimulated 4- to 10-fold by a sequence contained entirely within the dnaX reading frame. This region has been localized; at least a portion of the sequence (and perhaps the entire sequence) is located within a 31-bp region downstream of the dnaX promoter.
大肠杆菌的dnaX基因编码DNA聚合酶III的τ和γ亚基。该基因紧邻腺嘌呤补救基因apt的下游，位于orf12-recR、htpG和adk的上游。后三个基因分别参与重组、热休克和核苷酸生物合成。apt、dnaX和orf12-recR都有各自独立的启动子，前两个基因主要从这些独立的启动子进行表达。然而，使用核糖核酸酶E温度敏感突变体能够检测到从apt和dnaX启动子延伸至htpG的少量多顺反子信使RNA。有趣的是，dnaX弱启动子的转录受到一个完全包含在dnaX阅读框内的序列的刺激，刺激倍数为4至10倍。该区域已被定位；该序列的至少一部分（也许是整个序列）位于dnaX启动子下游的一个31碱基对区域内。
