In vivo, RNAi knockdown of LAF-1 results in the dissolution of P granules in the early embryo (microscopy). In vivo, endogenous LAF-1 exhibits a high degree of colocalization with PGL-1, the founding P granule protein. Upon lowering the salt concentration of solutions of purified LAF-1, the solution became cloudy. Solution turbidity is the result of condensed, highly spherical (morphology) droplets of LAF-1 as assessed by microscopy. At 125 mM NaCl, LAF-1 begins condensing at a critical protein concentration of roughly 800 nM, which is in the same order of magnitude as the estimated in vivo cytoplasmic concentration of LAF-1. LAF-1 droplets are homogeneous fluids with salt-dependent viscosity. Using a single-stranded poly-uridine model RNA (polyU 50), LAF-1 binds RNA with high affinity (KD ≈ 10 nM; physical interaction). Addition of 5 μM RNA into in vitro LAF-1 droplets results in a threefold decrease in the viscosity and more than twofold decrease in the FRAP recovery timescale of LAF-1, with an increase in the apparent diffusion coefficient. The C terminus is not required for phase separation, because truncated LAF-1 lacking the C terminus (ΔC) still forms droplets in vitro (particle size and count by microscopy), exhibiting a phase diagram similar to full-length LAF-1. In contrast, deletion of the RGG-rich N terminus (ΔRGG) results in no observable droplets, even up to concentrations as high as 250 μM. The isolated N-terminal RGG domain was alone sufficient for forming droplets (particle size and count by microscopy) (PMID:26015579).