The Ty1 integrase nuclear localization signal is necessary and sufficient for retrotransposon targeting to tRNA genes

Abstract

Integration of transposable elements into the genome is mutagenic. Mechanisms that target integration into relatively safe locations and minimize deleterious consequences for cell fitness have emerged during evolution. In budding yeast, the integration of the Ty1 LTR retrotransposon upstream of RNA polymerase III (Pol III)-transcribed genes requires the interaction between the AC40 subunit of Pol III and Ty1 integrase (IN1). Here we show that the IN1-AC40 interaction involves a short linker sequence in the bipartite nuclear localization signal (bNLS) of IN1. Mutations in this sequence do not impact the frequency of Ty1 retromobility, instead they decrease the recruitment of IN1 to Pol III-transcribed genes and the subsequent integration of Ty1 at these loci. The replacement of Ty5 retrotransposon targeting sequence by the IN1 bNLS induces Ty5 integration into Pol III-transcribed genes. Therefore, the IN1 bNLS is both necessary and sufficient to confer integration site specificity on Ty1 and Ty5 retrotransposons.