Escoubas J M, Prère M F, Fayet O, Salvignol I, Galas D, Zerbib D, Chandler M
Centre de Recherche de Biochimie et Génétique Cellulaire du CNRS, Toulouse, France.
EMBO J. 1991 Mar;10(3):705-12. doi: 10.1002/j.1460-2075.1991.tb08000.x.
The experiments reported here provide strong evidence indicating that the transposition frequency of the bacterial insertion sequence IS1 is determined principally by two IS1-specified proteins. The first, InsA, was previously shown to bind to the ends of the element and to act as a repressor. We present both physical and genetic evidence which reveals that the second, the InsAB' transposase, is a fusion of InsA with the product of a downstream reading frame, InsB'. Synthesis of this protein occurs by a -1 frameshift between the insA and insB' frames. It requires the presence of an intact retroviral-like frameshift signal composed of an A6C motif and a downstream region able to form several alternative secondary structures. In vivo studies show that IS1 transposition activity depends on the relative rather than on the absolute levels of InsA and InsAB'. The ratio is determined primarily at the translational level by frameshifting and appears to be relatively insensitive to large variations in levels of transcription. This novel homeostatic control could therefore protect IS1 from activation as a consequence of insertion into active transcription units.
本文报道的实验提供了有力证据，表明细菌插入序列IS1的转座频率主要由两种IS1指定的蛋白质决定。第一种是InsA，先前已证明它能结合元件末端并起阻遏作用。我们提供了物理和遗传证据，揭示了第二种蛋白质InsAB’转座酶是InsA与下游阅读框InsB’的产物的融合体。这种蛋白质的合成是通过insA和insB’阅读框之间的-1移码发生的。它需要存在一个完整的类似逆转录病毒的移码信号，该信号由一个A6C基序和一个能够形成几种替代二级结构的下游区域组成。体内研究表明，IS1转座活性取决于InsA和InsAB’的相对水平而非绝对水平。该比例主要在翻译水平上由移码决定，并且似乎对转录水平的大幅变化相对不敏感。因此，这种新型的稳态控制可以保护IS1不会因插入活性转录单元而被激活。
