Characterization by Electron Microscopy of Fused F-Prime Factors in Escherichia coli
Abstract
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.
- Publication:
-
Proceedings of the National Academy of Science
- Pub Date:
- July 1972
- DOI:
- 10.1073/pnas.69.7.1873
- Bibcode:
- 1972PNAS...69.1873P