Prion-like RNA binding proteins (RBPs) such as TDP43 and FUS are largely soluble in the nucleus but form solid pathological aggregates when mislocalized to the cytoplasm. What keeps these proteins soluble in the nucleus and promotes aggregation in the cytoplasm is still unknown. We report here that RNA critically regulates the phase behavior of prion-like RBPs. Low RNA/protein ratios promote phase separation into liquid droplets, whereas high ratios prevent droplet formation in vitro. Reduction of nuclear RNA levels or genetic ablation of RNA binding causes excessive phase separation and the formation of cytotoxic solid-like assemblies in cells. We propose that the nucleus is a buffered system in which high RNA concentrations keep RBPs soluble. Changes in RNA levels or RNA binding abilities of RBPs cause aberrant phase transitions.

Highlights d We examine the lipidome of the Gram-negative bacterium Methylobacterium extorquens d At least 11 out of 27 total lipid species contribute to adaptation to varying conditions d Remodeling of acyl chains is unevenly distributed across all lipid classes d Headgroup-specific acyl chain remodeling is implicated as an adaptive mechanism

Microorganisms can withstand a diversity of environmental stresses ranging from extreme temperatures to the immune defenses of multicellular organisms. The cell surface membrane serves as a first line of defense against environmental perturbations and the membrane's lipid composition is critical for stress resistance. On the one hand, the membrane must be robust enough to withstand chemical and physical challenges. On the other hand, the membrane must be fluid enough to support bioactivity. In eukaryotic organisms such as yeast, sterols play a crucial role in achieving a fluid yet mechanically robust cell surface membrane (Mouritsen & Zuckermann, 2004).

Evidence that microbial sulphate reduction is mainly responsible for the formation of the natron (hydrated Na2CO3) deposits in Wadi Natrûn is presented. The sulphate in the infiltrating water is reduced during passage through the surrounding waterlogged soil and the bicarbonate formed is later concentrated by evaporation in the lakes.