Barnett M J, Rushing B G, Fisher R F, Long S R
Department of Biological Sciences, Stanford University, California 94305, USA.
J Bacteriol. 1996 Apr;178(7):1782-7. doi: 10.1128/jb.178.7.1782-1787.1996.
In Rhizobium meliloti the syrM regulatory gene positively controls nod D3 and syrA, and nodD3 positively controls syrM and nod regulon genes such as nodABC, syrM and nodD3 are divergently transcribed and are separated by approximately 2.8 kb of DNA. The 885-bp SphI DNA fragment between syrM and nodD3 was subcloned and sequenced. Analysis of this intergenic region showed two open reading frames similar to those found in insertion elements of the IS3 family. We determined transcription initiation sites for both syrM and nodD3 using primer extension. The syrM transcription initiation site is 499 bp upstream of the syrM protein-coding region and downstream of a nod box which shows several differences from the R. meliloti nod box consensus sequence. We demonstrated binding of NodD3 to DNA containing the syrM nod box. The nodD3 start site maps 659 bp upstream of the nodD3 translation initiation site. A putative SyrM binding site was identified upstream of the nodD3 start site on the basis of sequence similarity to the upstream region of syrA, another locus regulated by SyrM.
在苜蓿根瘤菌中，syrM调控基因正向调控nodD3和syrA，而nodD3正向调控syrM和诸如nodABC等结瘤调节子基因。syrM和nodD3反向转录，且被大约2.8 kb的DNA分隔开。对syrM和nodD3之间885 bp的SphI DNA片段进行亚克隆并测序。对该基因间区域的分析显示出两个与IS3家族插入元件中发现的开放阅读框相似的开放阅读框。我们使用引物延伸法确定了syrM和nodD3的转录起始位点。syrM转录起始位点位于syrM蛋白质编码区上游499 bp处，且在一个与苜蓿根瘤菌结瘤框共有序列存在若干差异的结瘤框下游。我们证明了NodD3与含有syrM结瘤框的DNA结合。nodD3起始位点位于nodD3翻译起始位点上游659 bp处。基于与另一个受SyrM调控的位点syrA上游区域的序列相似性，在nodD3起始位点上游鉴定出一个假定的SyrM结合位点。
