Co-transcriptional Phase Separation of Nucleic Acids at Membrane Surfaces

Transcription is usually framed as information transfer, yet it also injects a new polymer into a crowded, confined environment. Here we demonstrate how spatial confinement to surfaces in a minimal membrane-bound transcription (MBT) system displays the physical consequences of RNA synthesis. Within a dense membrane-tethered DNA network, transcription drives co-transcriptional RNA phase separation: nascent RNA oligomerizes, gels and demixes from a surrounding fluid DNA phase, generating stable spatial patterns while mechanically remodeling the DNA layer. RNA gelation sequesters T7 RNA polymerase, whereas RNA-binding and translation-associated factors reverse gelation and restore fluidity. Thus, in the absence of downstream regulatory machinery, transcription under confinement is sufficient to trigger RNA condensation and nucleic-acid phase separation. The membrane as confining interface catalyzes the onset of DNA-RNA demixing and modulates the morphology of the resulting patterns. Since such large-scale spatial unmixing may be detrimental to cellular physiology, we suggest that one fundamental role of translation is to actively prevent condensation effects created by continuous RNA production.