How bacterial genes assemble into living droplets express
In a growing bacterium, genes that run protein factories don't drift solo. They clump into liquid droplets, like oily smears in water — no membranes, but sharp boundaries. The NusA protein fuels this condensation. When it piles up, it glues neighboring DNA stretches together, forcing them into foci. Physicists call this phase separation: like salad dressing splitting into oil and vinegar. That order means a drop in entropy — chaos — inside the cell. Protein chains built on carbon backbones form enough bonds to hold the droplets. But here's the twist: these droplets are alive — they pulse, assembling and dissolving in seconds. This solves a long-standing paradox: genes far apart on a long DNA thread, in experiments, always sit next to each other — droplets yank them into a single blob. And now it's clear: the same mechanism runs in our own cells, from immune cells to neurons.
Original abstract
as written by the authors arXiv:2604.02838
Along the bacterial chromosome, regions called rrn operons contain genes that are transcribed into ribosomal RNA. These operons are among the most transcriptionally active sites in the genome. It has been observed in E. coli that RNA polymerase (RNAP), while binding to these genetic loci along the chromosome during transcription, forms dense clusters, leading to spatial colocalization of the operons within the cell. Recent experimental evidence suggests that liquid-liquid phase separation contributes to the formation of RNAP clusters, with the antitermination factor NusA playing a key role. We present a simulation model to investigate the mechanisms underlying the formation of these biomolecular condensates. We propose that mutual attraction between NusA proteins, which exhibit a miscibility gap at higher concentrations, drives condensate formation via a polymer-assisted condensation pathway, and we demonstrate how these condensates promote the colocalization of rrn operons. Our results reconcile seemingly disparate experimental observations of chromosomal organization reported in fluorescence-based imaging and Hi-C experiments.
A single bacterial cell can hold up to 70,000 ribosomes — tiny factories that run nonstop, assembling proteins like cars on an assembly line.
In sci-fi, such droplets could become perfect nanobots — they self-assemble, self-dissolve, and need no external control.