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Institut für Pharmazeutische Biologie, Universität Frankfurt/M., Frankfurt, Germany,1 Lehrstuhl für Pharmazeutische Biologie, Universität Jena, Jena, Germany,2 Genome Analysis, Fritz Lipmann Institute, Jena, Germany,3 Zentrum für Arzneimittelforschung, Entwicklung und Sicherheit, Frankfurt, Germany4
Received 24 July 2006/ Returned for modification 18 August 2006/ Accepted 3 September 2006
In the compact Dictyostelium discoideum genome, non-long terminal repeat (non-LTR) retrotransposons known as TREs avoid accidental integration-mediated gene disruption by targeting the vicinity of tRNA genes. In this study we provide the first evidence that proteins of a non-LTR retrotransposon interact with a target-specific transcription factor to direct its integration. We applied an in vivo selection system that allows for the isolation of natural TRE5-A integrations into a known genomic location upstream of tRNA genes. TRE5-A frequently modified the integration site in a way characteristic of other non-LTR retrotransposons by adding nontemplated extra nucleotides and generating small and extended target site deletions. Mutations within the B-box promoter of the targeted tRNA genes interfered with both the in vitro binding of RNA polymerase III transcription factor TFIIIC and the ability of TRE5-A to target these genes. An isolated B box was sufficient to enhance TRE5-A integration in the absence of a surrounding tRNA gene. The RNA polymerase III-transcribed ribosomal 5S gene recruits TFIIIC in a B-box-independent manner, yet it was readily targeted by TRE5-A in our assay. These results suggest a direct role of an RNA polymerase III transcription factor in the targeting process.
Published ahead of print on 18 September 2006.
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