Erratum: Salt-Dependent Rheology and Surface Tension of Protein Condensates Using Optical Traps [Phys. Rev. Lett. 121, 258101 (2018)].

This corrects the article DOI: 10.1103/PhysRevLett.121.

Protein condensates as aging Maxwell fluids.

Protein condensates are complex fluids that can change their material properties with time. However, an appropriate rheological description of these fluids remains missing. We characterize the time-dependent material properties of in vitro protein condensates using laser tweezer-based active and microbead-based passive rheology.

Salt-Dependent Rheology and Surface Tension of Protein Condensates Using Optical Traps.

An increasing number of proteins with intrinsically disordered domains have been shown to phase separate in buffer to form liquidlike phases. These protein condensates serve as simple models for the investigation of the more complex membraneless organelles in cells. To understand the function of such proteins in cells, the material properties of the condensates they form are important.

A User's Guide for Phase Separation Assays with Purified Proteins.

The formation of membrane-less organelles and compartments by protein phase separation is an important way in which cells organize their cytoplasm and nucleoplasm. In vitro phase separation assays with purified proteins have become the standard way to investigate proteins that form membrane-less compartments. By now, various proteins have been purified and tested for their ability to phase separate and form liquid condensates in vitro.

RNA gets in phase.

Several neurological disorders are linked to tandem nucleotide repeat expansion in the mutated gene. Jain and Vale (2017. https://doi.

ATP as a biological hydrotrope.

Hydrotropes are small molecules that solubilize hydrophobic molecules in aqueous solutions. Typically, hydrotropes are amphiphilic molecules and differ from classical surfactants in that they have low cooperativity of aggregation and work at molar concentrations. Here, we show that adenosine triphosphate (ATP) has properties of a biological hydrotrope.

Polar Positioning of Phase-Separated Liquid Compartments in Cells Regulated by an mRNA Competition Mechanism.

P granules are non-membrane-bound RNA-protein compartments that are involved in germline development in C. elegans. They are liquids that condense at one end of the embryo by localized phase separation, driven by gradients of polarity proteins such as the mRNA-binding protein MEX-5.

A Liquid-to-Solid Phase Transition of the ALS Protein FUS Accelerated by Disease Mutation.

Many proteins contain disordered regions of low-sequence complexity, which cause aging-associated diseases because they are prone to aggregate. Here, we study FUS, a prion-like protein containing intrinsically disordered domains associated with the neurodegenerative disease ALS. We show that, in cells, FUS forms liquid compartments at sites of DNA damage and in the cytoplasm upon stress.

Characterization of structural and functional domains of the anillin-related protein Mid1p that contribute to cytokinesis in fission yeast.

Fission yeast cells depend on the anillin-related protein Mid1p for reliable cytokinesis. Insolubility limits the purification of full-length Mid1p for biophysical analysis, and lack of knowledge about the structural domains of Mid1p limits functional analysis. We addressed these limitations by identifying in a bacterial expression screen of random Mid1p fragments five soluble segments that can be purified and one insoluble segment.

Anillin-related protein Mid1p coordinates the assembly of the cytokinetic contractile ring in fission yeast.

In fission yeast cells cortical nodes containing the protein Blt1p and several kinases appear early in G2, mature into cytokinetic nodes by adding anillin Mid1p, myosin-II, formin Cdc12p, and other proteins, and condense into a contractile ring by movements that depend on actin and myosin-II. Previous studies concluded that cells without Mid1p lack cytokinetic nodes and assemble rings unreliably from myosin-II strands but left open questions. Why do strands form outside the equatorial region? Why is ring assembly unreliable without Mid1p? We found in Δmid1 cells that Cdc12p accumulates in cytokinetic nodes scattered in the cortex and produces actin filaments that associate with myosin-II, Rng2p, and Cdc15p to form strands located between the nodes.