Cellular surface breaks the symmetry of molecular diffusion across membrane. Here, we study how steric interactions between the surface and the bulk of cell-sized emulsion droplets alters gene expression emulated by a cell-free transcription/translation (TXTL) system. The concentration of synthesized reporter proteins in droplets of radius R shows an anomalous geometric scaling of R4 different from the expected size-dependence of R3. Given that TXTL becomes less efficient at thin surface layer, a mathematical model explains the anomalous size-dependence found in experiment. The surface of cell-sized compartment can thus play a regulatory role for cell-free gene expression.
Bibliographical noteFunding Information:
We thank Z. Izri for fruitfull discussion. This work was supported by Human Frontier Science Program Research Grant (RGP0037/2015) and JSPS KAKENHI (16H00805 Synergy of Structure and Fluctuation, 17H05234 Hadean Bioscience, and 17KT0025 Grant-in-Aid for Scientific Research (B) 17KT0025) from MEXT.