Abstract
An experimental model for cytoplasmic organization is presented. We demonstrate dynamic control over protein distribution within synthetic cells comprising a lipid bilayer membrane surrounding an aqueous polymer solution. This polymer solution generally exists as two immiscible aqueous phases. Protein partitioning between these phases leads to microcompartmentation, or heterogeneous protein distribution within the "cell" interior. This model cytoplasm can be reversibly converted to a single phase by slight changes in temperature or osmolarity, such that local protein concentrations can be manipulated within the vesicle interior.