LINE-1 ribonucleoprotein condensates bind DNA to enable nuclear entry during mitosis.

Area of Science:

• Genomics
• Molecular Biology
• Epigenetics

Background:

• Long interspersed nuclear element-1 (LINE-1) elements are autonomous retrotransposons comprising a significant fraction of the human genome.
• LINE-1 elements encode ORF1p and ORF2p proteins, critical for their mobility and contribution to genome evolution.
• ORF1p binds RNA and self-assembles onto LINE-1 RNA, forming ribonucleoprotein (RNP) condensates, whose function remains poorly understood.

Purpose of the Study:

• To elucidate the role of LINE-1 RNP condensates in the LINE-1 life cycle.
• To investigate the mechanism by which LINE-1 RNP condensates interact with host DNA.
• To determine the functional significance of RNP condensate DNA binding for LINE-1 retrotransposition.

Main Methods:

• In vitro reconstitution assays using DNA curtains to observe RNP condensate-DNA interactions.
• Cellular experiments to analyze RNP condensate localization and function within cells.
• Mutational analysis of LINE-1 components to assess the impact on DNA binding and retrotransposition.

Main Results:

• LINE-1 RNP condensates acquire DNA-binding activity specifically when the RNA is supersaturated with ORF1p.
• In mitotic cells, these RNP condensates exhibit binding to chromosomes.
• Disruption of DNA binding through mutational analysis impairs nuclear entry and LINE-1 retrotransposition.

Conclusions:

• ORF1p's crucial role is to facilitate the formation of RNP condensates.
• These condensates gain genome access via DNA binding during mitosis, following nuclear envelope breakdown.
• This mechanism is essential for LINE-1 retrotransposition and its impact on genome dynamics.