Originally published as Genetics Published Articles Ahead of Print on September 14, 2008.

Genetics, Vol. 180, 1367-1378, November 2008, Copyright © 2008
doi:10.1534/genetics.108.094318

Insulator and Ovo Proteins Determine the Frequency and Specificity of Insertion of the gypsy Retrotransposon in Drosophila melanogaster

Mariano Labrador1, Ky Sha2, Alice Li3 and Victor G. Corces4

Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218

4 Corresponding author: Department of Biology, Emory University, 1510 Clifton Rd. NE, Atlanta, GA 30322.
E-mail: vcorces{at}emory.edu

The gypsy retrovirus of Drosophila is quite unique among retroviruses in that it shows a strong preference for integration into specific sites in the genome. In particular, gypsy integrates with a frequency of >10% into the regulatory region of the ovo gene. We have used in vivo transgenic assays to dissect the role of Ovo proteins and the gypsy insulator during the process of gypsy site-specific integration. Here we show that DNA containing binding sites for the Ovo protein is required to promote site-specific gypsy integration into the regulatory region of the ovo gene. Using a synthetic sequence, we find that Ovo binding sites alone are also sufficient to promote gypsy site-specific integration into transgenes. These results indicate that Ovo proteins can determine the specificity of gypsy insertion. In addition, we find that interactions between a gypsy provirus and the gypsy preintegration complex may also participate in the process leading to the selection of gypsy integration sites. Finally, the results suggest that the relative orientation of two integrated gypsy sequences has an important role in the enhancer-blocking activity of the gypsy insulator.