Molecular Genetics of Prokaryotes Problem Set

Problem 5: DNA transfer by an F factor

Tutorial to help answer the question

An E. coli strain is F lac Z met bio. Cells from this strain are mixed with an E. coli strain that is lac Z met bio and carrying an F' episome with the Plac O lac Z DNA sequence on the episome, and cultured for several hours. Then cells were removed, washed, and transferred to minimal media containing lactose as the only sugar source. A few cells were able to grow on minimal media with lactose, and formed colonies. How did these few cells become lac Z met bio?

Tutorial

Conjugation

From question 4, we learned that E. coli bacteria can sexually conjugate and exchange genetic information. The genes that are required for conjugation, including the components of the pili on the surface of the male bacterium and the conjugation tube used for one-directional transfer of a copy of male DNA to the female cell, are encoded on the F' factor DNA of the male bacterium.

During conjugation, a copy of the F' factor DNA is transferred from the male to the female. The female becomes male following conjugation! An F' factor, also called an F' episome, contains additional genes besides those required for conjugation. In this experiment, the lac Z gene, encoding ß-galactosidase and the regulatory sequences of the operator are transferred with the F' factor. Transfer of an F' factor episome is a specialized type of conjugation known as sexduction.

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Updated: July 15, 1999
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