Genetic Analysis of the Transposable DNA Element IS2

在细菌和真核生物中已经确定了可以在基因组内移动的特定DNA序列。这些可转座的DNA元件不仅可以自行移动，还可以促进各种自发突变，这些突变可以改变细胞的结构组织，通常还会改变细胞遗传信息的表达。虽然由此产生的遗传多样性在进化意义上可能被证明是有益的，但一些转座子诱导的突变可能是非常有害的，比如当癌基因被激活，细胞转化为肿瘤状态时。最简单的转座元件是细菌插入序列(IS元件)。本实验室将重点研究一种这样的元件，IS2，它存在于大肠杆菌K-12的染色体中，但不存在于E.coliC中。IS2可以转座到新的位置，导致新插入的IS2元件附近的基因表达减少或增加。我们的研究已经确定了IS2中的两个区域，它们编码了IS2转座和切除所需的或调节的因子。这些结果表明，IS2可能通过一种保守的机制转位，包括切除(伴随着供体“染色体”的存活)和在新的遗传位点重新整合IS2。我们将把我们的研究重点放在检验这一假设上：确定假定的蛋白质产物以及每个蛋白质产物在IS2切除和/或转座中的作用。此外，我们将研究IS2编码蛋白的相对表达水平如何在转录或翻译水平上进行调节。

Specific sequences of DNA which can move within the genome have been identified in bacteria and eukaryotes. These transposable DNA elements not only move themselves but also facilitate a variety of spontaneous mutations which can alter the structural organization and often the expression of a cell's genetic information. While the resulting genetic diversity may prove beneficial in an evolutionary sense, some transposon-induced mutations may be quite detrimental as when oncogenes are activated and cells become transformed to a neoplastic state. Among the simplest transposable elements are the bacterial insertion sequences (IS elements). This laboratory will focus studies on one such element, IS2, which is present in the chromosome of Escherichia coli K-12 but absent from E. coli C. IS2 can transpose to new sites causing either decreased or increased expression of genes adjacent to the newly inserted IS2 element. Our studies have identified two regions within IS2 that encode factors required for, or regulating, both transposition and excision of IS2. These results suggest that IS2 may transpose by a conservative mechanism involving excision (with survival of the donor "chromosome") and reintegration of IS2 at a new genetic locus. We will focus our studies on testing this hypothesis: to identify the presumptive protein products and the role for each in IS2 excision and/or transposition. In addition we will examine how the relative level of expression of the IS2 encoded proteins may be regulated at transcriptional or translational levels.