Willcox, S. | bioRxiv Science

bioRxiv2026

cGAS bends unpaired DNA to form an unconventional structure that hyperactivates the innate immune response

cGAS is a pattern-recognition receptor for dsDNA and forms 2cGAS:2DNA dimers followed by oligomerization into phase-separated condensates when fully-complementary DNA is studied. However, many DNAs are not fully complementary. We report that DNA with unpaired regions such as those found during transcription, recombination or replication (designated as bubble-DNA, Bu-DNA) causes cGAS hyper-activation. Hyperactivation is observed by Bu-DNA embedded in linear DNA, circular DNA, plasmid DNA and mitochondria DNA. Bu-DNA binds significantly more tightly to the cGAS catalytic domain than paired-DNA but suppresses condensation. Cryo-EM and single-molecule FRET reveal that cGAS forms 2cGAS:1DNA complexes by bending Bu-DNA into a V-shape using the unpaired region as a hinge, limiting its oligomeric state. This uncovers a novel mode of cGAS activation attributed to pattern diversity within pattern ligands.

immunology↗

bioRxiv2024

The valine-arginine dipeptide repeat protein encoded by mammalian telomeric RNA appears highly expressed in mitosis and may repress global translation

Translation of mammalian telomeric G-rich RNA via the Repeat Associated non-AUG translation mechanism can produce two dipeptide repeat proteins: repeating valine-arginine (VR) and repeating glycine-leucine (GL). Their potentially toxic nature suggests that one or both must play a needed role in the cell. Using light microscopy combined with antibody staining we discovered that cultured human cells stain brightly for VR during mitosis with VR staining co-localizing with ribosomes. In vitro, VR protein represses translation in a firefly luciferase assay. Affinity purification combined with mass spectrometry identified ribosomal proteins as the major class of VR interacting proteins. Extension to mouse embryonic cerebral cortical development showed strong staining in the ventricular zone where high mitotic index neural progenitor cells proliferate and in the cortical plate where new neurons settle. These observations point to VR playing a key role in mitosis very possibly depressing global translation, a role mediated by the telomere. TeaserThe telomeric valine-arginine dipeptide repeat protein is highly expressed in mitotic cells in culture and in mouse embryonic neural tissue.

molecular biology↗