Recently, the important role of microphase separation in living cells has been attracting considerable interest in relation to cell organization and function. For example, many studies have focused on liquid-liquid phase separation (LLPS) as a very plausible mechanism for the presence of membraneless organelles. To confirm the role of phase separation in living cells, experimental studies on models and/or reconstructed systems are needed. In this short review, we discuss current paradigms of LLPS and provide some example "review data" to demonstrate particular points relating to the specific localization of biological macromolecules like DNAs and actin proteins with spontaneous domain formation in microdroplets emerging in an aqueous two-phase system (ATPS) (we use polyethylene glycol (PEG)/dextran (DEX)-a binary polymer solution). We also suggest that phase separation and transition may play basic roles in regulation of the biochemical reactivity of individual long genomic DNAs.
Keywords: Aqueous two-phase system; DNA condensation; Depletion effect; Macromolecular crowding; Microcompartmentalization; Phase transition.