Biology subjects

Calmels, C.

Publications and source records attributed to Calmels, C..

2 recordsLinked to original sources

bioRxiv2025

Timed chromatin invasion during mitosis governs prototype foamy virus integration site selection and infectivity

Selection of a suitable chromatin environment during retroviral integration is a tightly regulated and multilayered process that involves interplay between viral and host factors. However, whether intrinsic chromatin dynamics during mitosis modulate retroviral genome invasion is currently poorly described. Direct interaction between the spumaretrovirus prototype foamy virus (PFV) Gag protein and cellular chromatin has been described as a major determinant for integration site selection. A previous Gag chromatin-binding site (CBS)-nucleosome co-crystal structure revealed an interaction with the histone H2A-H2B acidic patch via a highly conserved arginine anchor residue. Yet, the molecular mechanisms regulating Gag-chromatin capture during PFV infection remain obscure. Here, we investigated the kinetics of Gag-chromatin interactions during mitosis and proviral integration of PFV-infected synchronized cells. Using Gag CBS variant viruses, we showed that alteration of Gag affinity for nucleosome binding induced untimely chromatin tethering during mitosis, decreased infectivity and redistributed viral integration sites to markers associated with late replication timing of host chromosomes. Mutant Gag proteins were moreover defective in their ability to displace the histone H4 tail from the nucleosome acidic patch of highly condensed mitotic chromatin. These data indicate that the mitotic chromatin landscape during Gag-nucleosome interactions hosts PFV integration site selection determinants and that spumaretroviruses evolved high-affinity chromatin binding to overcome early mitosis chromatin condensation for optimal viral DNA tethering, integration and infection.

microbiology↗

bioRxiv2020

Analysis of the intrinsic chromatin binding property of HIV-1 integrase and its regulation by LEDGF/p75 using human chromosomes spreads

Retroviral integration requires the stable insertion of the viral genome into the host chromosomes. During this process, the functional integration complex must associate with cellular chromatin via the interaction between retroviral integrase and nucleosomes. The final association between the HIV-1 integration complex and the nucleosomal target DNA remains unclear and may involve the chromatin-binding properties of both the retroviral integrase and its cellular cofactor LEDGF/p75. To date, there is no experimental system allowing the direct monitoring of this protein association with chromatin to depict the molecular mechanism of this process fully. To investigate this and understand the LEDGF/p75-mediated chromatin tethering of HIV-1 integrase further, we used both biochemical approaches and an unedited chromosome-binding assays. Our study revealed that retroviral IN has an intrinsic ability to bind and recognize specific chromatin regions even in the absence of its cofactor. We also showed that this integrase chromatin-binding property was modulated by the interaction with its cofactor LEDGF/p75, which redirected the enzyme to alternative chromatin regions. Using these approaches, we also better determined the chronology of efficient LEDGF/p75-mediated targeting of HIV-1 integrase to chromatin. In addition to supporting a chromatin-binding function of the integrase protein acting in concert with LEDGF/p75 for the optimal association with the nucleosomal substrate, our work precisely elucidates the mechanism of action of LEDGF/p75 in this crucial integration step.

microbiology↗