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Transposon Tn3, 1973 to 1980, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555818340/9781555810825_Chap03-1.gif /docserver/preview/fulltext/10.1128/9781555818340/9781555810825_Chap03-2.gifAbstract:
This chapter reviews the work on transposable drug resistance, specifically, the ampicillin resistance transposon Tn3, that was carried out in Stanley Falkow's laboratory. It starts by describing the events that occurred in the fall of 1973 and ends with the departure of Ron Gill from the laboratory in 1980. The researchers assumed that the gene for ampicillin-resistant (Apr) would show observable cross-hybridization, if there were any DNA identity. The observation that the same β-lactamase gene and some of its flanking DNA was moving from plasmid to plasmid seemed clear, but one could imagine many different mechanisms. At that time it was not clear whether this phenomenon was peculiar to Tn3 or could be generalized to other antibiotic resistance genes. Several of the antibiotic-resistant isolates were compared by DNA-DNA heteroduplex analysis. Different fractions from the gradient were used to transform Escherichia coli by the CaCl2 method, and recombinants were found at an intermediate density. The insertions were mapped by heteroduplex analysis and electron microscopy following cleavage with EcoRI provided by Herb Boyer (EcoRI cleaved the target molecule once). The electron microscopic data and the results of restriction enzyme analysis were both consistent with the interpretation that complementation of these mutants resulted in a single insertion into the target plasmid.