2011), salt concentrations (Fig. S5), nucleotides (Table S2), and the molecular weight of the pLys (Table S2). RNA oligomers partitioned strongly into the complex-enriched phase to a degree that was comparable to that of the DEAE-dextran/PEG system (Table S1). RNA Retention in ATPS and Coacervate Droplets We sought to determine the ability of ATPS and coacervate droplets to retain RNA in a manner similar to fatty acid based vesicles find more by preparing droplets into which a fluorescently labeled RNA 15-mer oligonucleotide had partitioned. We then used
fluorescence recovery after photobleaching (FRAP) microscopy to analyze the rates at which the RNA moved from the bulk phase into photo-bleached droplets. At steady state, this would be equivalent to the rate at which RNA diffused out of droplets into the bulk phase (and then into other droplets). We acquired and analyzed fluorescence recovery data for fluorescently labeled RNA in droplets from four systems (Table S3): 16 % dextran/10 % PEG (Fig. 1a, Movie S1), 25 % DEAE-dextran/25 % PEG (Fig. 1b, Movie S2), 16 % dextran-sulfate/10 % PEG (Fig. 1c, Movie S3), and 30 mM ATP/2 % pLys (Fig. 1d, Movie S4) (all percentages w/v). The sizes of FK506 droplets ranged from 1 to 5 μm in diameter (Fig. S6), similar in size to proposed fatty acid vesicle based protocell model systems (Adamala and Szostak 2013a), up to 50–75 μm in diameter (Fig. 1c),
similar in size to giant unilamellar vesicles (Dimova et al. 2006). Fig. 1 Rapid exchange of RNA oligomers between ATPS and coacervate droplets and the surrounding bulk phase. Representative confocal fluorescence images showing RNA enriched droplets (green) are shown at left. Normalized fluorescence
recovery after photobleaching (FRAP) recovery curves are shown at right. All samples contained 5 μM 5′-6-FAM-labeled RNA 15-mer (5′-CCAGUCAGUCUACGC-3′) in: (a) 16 % w/v dextran 9-11 kDa/10 % w/v PEG 8 kDa in 50 mM Tris-Cl pH 8 and 100 mM NaCl (indicated droplet 25 μm diameter), (b) 25 % w/v DEAE-dextran >500 kDa/25 % w/v PEG 8 kDa in 100 mM Tris-Cl pH 8 with the GODCAT (glucose oxidase/catalase) system (Methods) (indicated droplet 9.5 μm diameter), (c) 16 % w/v dextran-sulfate 9-20 kDa/10 % w/v PEG 8 kDa in 50 mM Tris-Cl pH 8 and 100 mM NaCl (indicated droplet 44 μm diameter), (d) oxyclozanide 30 mM ATP/2 % w/v pLys 4-15 kDa in 100 mM Tris-Cl pH 8 with the GODCAT system (Methods) (indicated droplet 7.5 μm diameter). See Movies S1-S4 for respective FRAP movies. Each curve was normalized to the intensities of a non-bleached droplet and the background within the same frame, to correct for photobleaching during sampling, as well as to its initial intensity, to account for variable photobleaching before the recovery step across runs (Supplementary Information). Data were fit to a single exponential to determine time constants (τ) and half-lives (t1/2) for fluorescence recovery (Supplementary Information).