Gene regulation

Stigler lab in collaboration with the Holt lab decipher that LINE-1 ORF1p forms super-saturated co-condensates with RNA that enable DNA binding and nuclear entry during mitosis.

Abstract:

Long Interspersed Nuclear Element-1 (LINE-1) is an autonomous retrotransposon that makes up a significant portion of the human genome, contributing to genetic diversity and genome evolution. LINE-1 encodes two proteins, ORF1p and ORF2p, both essential for successful retrotransposition. ORF2p has endonuclease and reverse transcription activity, while ORF1p binds RNA. Many copies of ORF1p assemble onto the LINE-1 RNA to form a ribonucleoprotein (RNP) condensate. However, the function of these condensates in the LINE-1 life cycle remains unclear. Using reconstitution assays on DNA curtains, we show that L1 RNP condensates gain DNA binding activity only when RNA is super-saturated with ORF1p. In cells, L1 RNP condensates bind to chromosomes during mitosis. Mutational analysis reveals that DNA binding is crucial for nuclear entry and LINE-1 retrotransposition activity. Thus, a key function of ORF1p is to form an RNP condensate that gains access to the genome through DNA binding upon nuclear envelope breakdown.

Original Publication:

LINE-1 ribonucleoprotein condensates bind DNA to enable nuclear entry during mitosis
Sarah Zernia, Farida Ettefa, Srinjoy Sil, Cas Koeman, Joëlle Deplazes-Lauber, Marvin Freitag, Liam J Holt, Johannes Stigler
Science Advances 2025. https://doi.org/10.1126/sciadv.adt9318