Abstract
Although the two F′ elements, F57 (carrying his+) and KLF1 (carrying leu+), cannot normally coexist in the same cell, crosses between RecA- strains of Escherichia coli carrying these two elements gave rise, at a low frequency, to progeny carrying both the his+ and leu+ markers in an extrachromosomal state. Genetic studies showed that the his+ and leu+ markers were now linked, and centrifugation studies of F′ DNA isolated from these strains confirmed the presence of a new species of DNA molecule of altered size. It is proposed that the his+ and leu+ genes in these strains are covalently linked on a single “fused” F′ element.
Keywords: sucrose gradient centrifugation, extrachromosomal DNA
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Selected References
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