Effect of Liposome Size on Internal RNA Replication Coupled with Replicase Translation

Cell membranes inhibit the diffusion of intracellular materials, and compartment size can strongly affect the intracellular biochemical reactions. To assess the effect of the size of microcompartments on intracellular reactions, we constructed a primitive cell model consisting of giant liposomes and a translation-coupled RNA replication (TcRR) system. The RNA was replicated by Qβ replicase, which was translated from the RNA in giant liposomes encapsulating the cell-free translation system. A reporter RNA encoding the antisense strand of β-glucuronidase was introduced into the system to yield a TcRR read-out (green fluorescence). We demonstrate that TcRR was hardly detectable in larger liposomes (230 fL) but was more effective in smaller (7.7 fL) liposomes. Our experimental and theoretical results show that smaller microcompartments considerably enhance TcRR because the synthesized molecules, such as RNA and replicases, are more concentrated in smaller liposomes.