Luque Ignacio, Andújar Alfonso, Jia Lin, Zabulon Gérald, de Marsac Nicole Tandeau, Flores Enrique, Houmard Jean
Dpto Fisiología, Genética y Microbiología, Facultad de Ciencias, Universidad de Alicante, Campus de San Vicente, Alicante 03080, Spain.
Mol Microbiol. 2006 Jun;60(5):1276-88. doi: 10.1111/j.1365-2958.2006.05170.x.
The genome of Tolypothrix sp. PCC 7601 carries two copies of a novel insertion sequence, ISTosp1. One of the two copies is located upstream of the gene encoding glutamyl-tRNA synthetase, an enzyme playing a key role in protein and pigment synthesis. The tnpA gene of the IS element and gltX were co-transcribed and their expression was transiently upregulated upon retrieval of the ammonium source irrespective of whether nitrate or no nitrogen source were available. The second copy is also transcribed and shows a similar regulatory pattern. Structural elements of the promoter (-10 and -35 sequences) directing the expression of the tnpA-gltX operon have been localized within the IS. Regulatory sequences involving the NtcA transcription factor in the control of tnpA-gltX expression were found both within and in sequences upstream of the insertion element. The expression of gltX in a closely related cyanobacterium, Nostoc sp. PCC 7120, which lacks the insertion upstream of gltX, decreased upon ammonium retrieval, a regulatory pattern that markedly differs from that observed in Tolypothrix sp. PCC 7601. ISTosp1 constitutes a good example of how cells can make use of a transposable element to evolve an original regulatory mechanism.
颤藻属（Tolypothrix）菌株PCC 7601的基因组携带一种新型插入序列ISTosp1的两个拷贝。这两个拷贝之一位于编码谷氨酰胺-tRNA合成酶的基因上游，该酶在蛋白质和色素合成中起关键作用。IS元件的tnpA基因和gltX基因共同转录，并且无论是否有硝酸盐或无氮源，在恢复铵源后它们的表达都会瞬时上调。第二个拷贝也被转录并显示出类似的调控模式。指导tnpA - gltX操纵子表达的启动子的结构元件（-10和-35序列）已定位在IS内。在插入元件内部和上游序列中都发现了涉及NtcA转录因子控制tnpA - gltX表达的调控序列。在缺乏gltX上游插入序列的密切相关蓝细菌 Nostoc sp. PCC 7120中，gltX的表达在恢复铵后下降，这种调控模式与在颤藻属菌株PCC 7601中观察到的明显不同。ISTosp1是细胞如何利用转座元件进化出原始调控机制的一个很好的例子。
