Distal spinal muscular atrophy type 1 (DSMA1) is an autosomal recessive disease that is clinically characterized by distal limb weakness and respiratory distress. In this disease, the degeneration of alpha-motoneurons is caused by mutations in the immunoglobulin mu-binding protein 2 (IGHMBP2). This protein has been implicated in DNA replication, pre-mRNA splicing and transcription, but its precise function in all these processes has remained elusive. We have purified catalytically active recombinant IGHMBP2, which has enabled us to assess its enzymatic properties and to identify its cellular targets. Our data reveal that IGHMBP2 is an ATP-dependent 5' --> 3' helicase, which unwinds RNA and DNA duplices in vitro. Importantly, this helicase localizes predominantly to the cytoplasm of neuronal and non-neuronal cells and associates with ribosomes. DSMA1-causing amino acid substitutions in IGHMBP2 do not affect ribosome binding yet severely impair ATPase and helicase activity. We propose that IGHMBP2 is functionally linked to translation, and that mutations in its helicase domain interfere with this function in DSMA1 patients.

Interacting Bosons in artificial lattices have emerged as a modern platform to explore collective manybody phenomena and exotic phases of matter as well as to enable advanced on-chip simulators. On chip, exciton–polaritons emerged as a promising system to implement and study bosonic non-linear systems in lattices, demanding cryogenic temperatures. We discuss an experiment conducted on a polaritonic lattice at ambient conditions: We utilize fluorescent proteins providing ultra-stable Frenkel excitons. Their soft nature allows for mechanically shaping them in the photonic lattice. We demonstrate controlled loading of the coherent condensate in distinct orbital lattice modes of different symmetries. Finally, we explore the self-localization of the condensate in a gap-state, driven by the interplay of effective interaction and negative effective mass in our lattice. We believe that this work establishes organic polaritons as a serious contender to the well-established GaAs platform for a wide range of applications relying on coherent Bosons in lattices.

The assembly of spliceosomal U snRNPs depends on the coordinated action of PRMT5 and SMN complexes in vivo. These trans-acting factors enable the faithful delivery of seven Sm proteins onto snRNA and the formation of the common core of snRNPs. To gain mechanistic insight into their mode of action, we reconstituted the assembly machinery from recombinant sources. We uncover a stepwise and ordered formation of distinct Sm protein complexes on the PRMT5 complex, which is facilitated by the assembly chaperone pICln. Upon completion, the formed pIClnSm units are displaced by new pICln-Sm protein substrates and transferred onto the SMN complex. The latter acts as a Brownian machine that couples spontaneous conformational changes driven by thermal energy to prevent mis-assembly and to ensure the transfer of Sm proteins to cognate RNA. Investigation of mutant SMN complexes provided insight into the contribution of individual proteins to these activities. The biochemical reconstitution presented here provides a basis for a detailed molecular dissection of the U snRNP assembly reaction.

The strong light-matter coupling of a microcavity mode to tightly bound Frenkel excitons in organic materials emerged as a versatile, room-temperature compatible platform to study nonlinear many-particle physics and bosonic condensation. However, various aspects of the optical response of Frenkel excitons in this regime remained largely unexplored. Here, we utilize a hemispheric optical cavity filled with the fluorescent protein mCherry to address two important questions in the field of room-temperature polariton condensates. First, combining the high quality factor of the microcavity with a well-defined mode structure allows us to provide a definite answer whether temporal coherence in such systems can become competitive with their low-temperature counterparts. We observe highly monochromatic and coherent light beams emitted from the condensate, characterized by a coherence time greater than 150 ps, which exceeds the polariton lifetime by two orders of magnitude. Second, the high quality of our device allows to sensibly trace the emission energy of the condensate, and thus to establish a fundamental picture which quantitatively explains the core nonlinear processes yielding the characteristic density-dependent blueshift. We find that the energy shift of Frenkel excitonpolaritons is largely dominated by the reduction of the Rabi-splitting due to phase space filling effects, which is influenced by the redistribution of polaritons in the system. While our finding of highly coherent condensation at ambient conditions addresses the suitability of organic polaritonics regarding their utilization as highly coherent room temperature polariton lasers, shedding light on the non-linearity is of great benefit towards implementing non-linear devices, optical switches, and lattices based on exciton-polaritons at room temperature.

Interacting bosonic particles in artificial lattices have proven to be a powerful tool for the investigation of exotic phases of matter as well as phenomena resulting from non-trivial topology. Exciton-polaritons, bosonic quasi-particles of light and matter, have shown to combine the on-chip benefits of optical systems with strong interactions, inherited form their matter character. Technologically significant semiconductor platforms, however, strictly require cryogenic temperatures for operability. In this paper, we demonstrate exciton-polariton lasing for topological defects emerging form the imprinted lattice structure at room temperature. We utilize a monomeric red fluorescent protein derived from DsRed of Discosoma sea anemones, hosting highly stable Frenkel excitons. Using a patterned mirror cavity, we tune the lattice potential landscape of a linear Su-Schrieffer-Heeger chain to design topological defects at domain boundaries and at the edge. In spectroscopic experiments, we unequivocally demonstrate polariton lasing from these topological defects. This progress promises to be a paradigm shift, paving the road to interacting Boson many-body physics at ambient conditions.