LTR retrotransposons are generally repressed in mammals and do not lead to new genome insertions. Their transcription reactivation is a feature of malignant cells and aging, and is associated with genome instability. Retrotransposon RNA is a key intermediate in the replication of LTR retrotransposons as it serves as template for both translation and reverse-transcription. Yet, we know little about the proteome involved in RNA retrotransposon fate. Moreover, while genomic instability is in part due to retrotransposition, it remains unclear whether the presence of the transcript itself also participates, for instance by inducing replication stress or nucleic acid secondary structures. Therefore, proteins that bind LTR retrotransposon RNA could be pivotal in genome instability linked to retrotransposon activity.

Using the LTR retrotransposon model Ty1 in S. cerevisiae, we have set up a new method named Comprehensive Identification of RNA-binding Proteins by Mass Spectrometry (ChIRP-MS) to identify such Ty1 RNA-binding proteins. Based on stringent criteria, we selected a total of 29 candidates associated with Ty1 RNA, 66% of which had never before been identified as regulators of retrotransposition. We have begun to study the impact of Ty1 RNA-binding proteins on Ty1 activity by constructing deletion mutants of selected candidates. We will present a first analysis of these mutants on the different steps of the Ty1 cycle. Our study is promising in deciphering the function of these candidates on Ty1 activity and genome instability.