Barnett M J, Long S R
Department of Biological Sciences, Stanford University, CA 94305, USA.
Mol Plant Microbe Interact. 1997 Jul;10(5):550-9. doi: 10.1094/MPMI.1997.10.5.550.
The Rhizobium meliloti SyrM protein activates transcription of nodD3 and syrA. Regulation of syrM is complex and may involve as yet undiscovered genes. Here we report the isolation of insertion mutants showing increased expression of a syrM-gusA gene fusion. Characterization of one mutant strain, designated SYR-B, revealed a mutation consisting of a transposon insertion linked to a large deletion. The corresponding wild-type DNA was cloned as a 5.3-kb BamHI fragment. Genetic and physical analysis of this DNA demonstrated that an open reading frame (ORF) near one end of the fragment, encoding the 16.5-kDa SyrB protein, is responsible for the repression of syrM activity. Results of complementation experiments with the 5.3-kb BamHI DNA led us to hypothesize that other genes within this DNA fragment interfere with the expression or activity of SyrB. Our analysis showed that the region upstream of syrB contains three ORFs. One ORF is similar to the Ros repressor of Agrobacterium tumefaciens and the MucR repressor of R. meliloti.
苜蓿中华根瘤菌SyrM蛋白可激活nodD3和syrA的转录。syrM的调控较为复杂，可能涉及尚未发现的基因。在此，我们报道了插入突变体的分离，这些突变体表现出syrM - gusA基因融合体表达增加。对其中一个命名为SYR - B的突变菌株进行表征，发现其突变由一个与大片段缺失相连的转座子插入组成。相应的野生型DNA被克隆为一个5.3 kb的BamHI片段。对该DNA的遗传和物理分析表明，该片段一端附近的一个开放阅读框（ORF）编码16.5 kDa的SyrB蛋白，它负责抑制syrM的活性。用5.3 kb的BamHI DNA进行互补实验的结果使我们推测，该DNA片段中的其他基因会干扰SyrB的表达或活性。我们的分析表明，syrB上游区域包含三个ORF。其中一个ORF与根癌土壤杆菌的Ros阻遏物和苜蓿中华根瘤菌的MucR阻遏物相似。
