Program > Browse abstracts by speaker > Capuzzi Beatrice

To maintain host cell survival and ensure their own propagation, many transposable elements (TEs) have evolved the capacity of integrating into specific regions of the genome. This is the case of the Ty1 LTR retrotransposon model of S. cerevisiae, which targets regions upstream of Pol III-transcribed genes by means of a direct interaction between its integrase (IN1) and the RNA Polymerase III (Pol III) subunit AC40 (Bridier-Nahmias et al,.2015; Asif-Laidin et al.,2020). Strikingly, the loss of IN1/AC40 interaction redirects Ty1 insertions to subtelomeres, which are gene-poor regions enriched in non-essential stress-responsive genes. While the IN1/AC40 interaction has been delineated at the atomic level (Nguyen et al.,2023), the molecular mechanism of targeted integration at subtelomeric loci has yet to be elucidated. Furthermore, an unexplained mechanism drives Ty1 insertions to two specific hotspots on the nucleosomal DNA (Baller et al.,2012; Mularoni et al.,2012). Altogether, these observations strongly suggest that Ty1 integration pattern is most likely the result of multiple influences, including chromatin structure.

To identify novel factors that contribute to Ty1 integration site selection, we first confronted our libraries of Ty1 de novo insertion events with the genome-wide distribution of known chromatin features. We observed a striking correlation between Ty1 insertions and the presence of the H2A.Z variant of the histone H2A, suggesting that H2A.Z could contribute to direct Ty1 integration. However, our data indicated that H2A.Z rather prevents Ty1 integration at both tDNAs and subtelomeric loci, pointing to a more complex role of H2A.Z in Ty1 integration site selection. In a second approach, we have set up a proximity-dependent biotinylation proteomic screen to identify new partners of Ty1 integrase. By comparing the interactome of IN1 wild-type and loss-of-interaction mutant, we expect to identify common and specific cofactors of Ty1 integration site selection that together contribute to the specific targeting of Ty1.