Genetic Analysis of the Transposable DNA Element IS2

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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.