Droplets that decay, droplets that fährt: Restriction enzymes induce degradation, bubbling and propulsion in a DNA liquid phase

Multi-armed DNA particles (‘nanostars’) can be engineered to have weak inter-particle attractions, causing them to phase separate into liquid droplets. We are motivated to study this system both on the general grounds that bio-macromolecular liquids are interesting, and with the specific idea of using it to create a chromatin-inspired active matter system. To that end, we studied the interactions of proteins with DNA nanostar droplets, particularly measuring droplet degradation by DNA-cleaving restriction enzymes. Despite the droplet’s small DNA volume fraction, enzyme degradation occurred primarily on surface of droplets, likely because enzyme transport was arrested by binding of the protein to the DNA. The degradation rate was surprisingly insensitive to variations in the number of restriction sites, but did vary with the strength of bonds between DNA particles. With certain tricks it was possible to force the enzyme inside the droplet, which caused the enzyme to carve out vacuoles that rose to the droplet surface and popped, driving droplet motion. I will discuss potential mechanisms behind this enzyme-induced motility.