Characterization by Electron Microscopy of Fused F-Prime Factors in Escherichia coli

AUTOR(ES)

Palchaudhuri, S. R.

RESUMO

During previous attempts to find mutants in which incompatibility between two F-prime (F′) factors of E. coli is abolished, we found that two F′ factors harbored in the same cell occasionally recombined to form a single genetic unit. Thus, a fused F′trp+arg+ factor was obtained from a mating of a strain carrying recA F′trp+ with a strain carrying recA F′arg+. In the present paper physical fusion of the two F′ factors, inferred from genetic studies, is confirmed by electron microscopy. F DNA was extracted, after detergent lysis, from four fused F′ strains: the parental F′trp+ and F′arg+ strains and three F+ strains. This supercoiled DNA was separated on ethidium bromide-cesium chloride gradients and converted to the open circular from before electron microscopy. The contour lengths in μm of the various DNA preparations were: F′trp+, 59.4; F′arg+, 33.2; the four F′trp+arg+ factors, 38.5, 39.6, 63.2, and 73.5: the three F factors, 31.1, 31.1, and 31.0. Thus, different fused F′ factors formed from the same parental F′ factors vary in length, but are shorter than the sum of the parental F′ factors.

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