The compaction of chromatin into mitotic chromosomes is essential for faithful transmission of the genome during cell division. In eukaryotes, chromosome morphogenesis is regulated by the condensin complex, though the exact mechanism used to target condensin to chromatin and initiate condensation is not understood. Here, we reveal that condensin contains an intrinsically disordered region (IDR) that modulates its association with chromatin in early mitosis and exhibits phase separation. We describe DNA-binding motifs within the IDR that, upon deletion, inflict striking defects in chromosome condensation and segregation, ill-timed condensin turnover on chromatin, and cell death. Importantly, we demonstrate that the condensin IDR can impart cell cycle regulatory functions when transferred to other subunits within the complex, indicating its autonomous nature. Collectively, our study unveils the molecular basis for the initiation of chromosome condensation in early mitosis and how this process ultimately promotes genomic stability and faultless cell division.

In cells, mRNAs are transported to and positioned at subcellular areas to locally regulate protein production. Recent studies have identified the kinesin-3 family member motor protein KIF1C as an RNA transporter. However, it is not clear how KIF1C interacts with RNA molecules. Here, we show that the KIF1C C-terminal tail domain contains an intrinsically disordered region (IDR) that drives liquid-liquid phase separation (LLPS). KIF1C forms dynamic puncta in cells that display physical properties of liquid condensates and incorporate RNA molecules in a sequence-selective manner. Endogenous KIF1C forms condensates in cellular protrusions, where mRNAs are enriched in an IDR-dependent manner. Purified KIF1C tail constructs undergo LLPS in vitro at near-endogenous nM concentrations and in the absence of crowding agents and can directly recruit RNA molecules. Overall, our work uncovers an intrinsic correlation between the LLPS activity of KIF1C and its role in mRNA positioning. In addition, the LLPS activity of KIF1C\'s tail represents a new mode of motor-cargo interaction that extends our current understanding of cytoskeletal motor proteins.

Spindlin1 (SPIN1) is a unique multivalent histone modification reader that plays a role in ribosomal RNA transcription, chromosome segregation, and tumorigenesis. However, the function of the extended N-terminal region of SPIN1 has remained unclear. Here, we discovered that SPIN1 can form phase-separated and liquid-like condensates both in vitro and in vivo through its N-terminal intrinsically disordered region (IDR). The phase separation of SPIN1 recruits the histone methyltransferase MLL1 to the same condensates and enriches the H3K4 methylation marks. This process also facilitates the binding of SPIN1 to H3K4me3 and activates tumorigenesis-related genes. Moreover, SPIN1-IDR enhances the genome-wide chromatin binding of SPIN1 and facilitates its localization to genes associated with the MAPK signaling pathway. These findings provide new insights into the biological function of the IDR in regulating SPIN1 activity and reveal a previously unrecognized role of SPIN1-IDR in histone methylation readout. Our study uncovers the crucial role of appropriate biophysical properties of SPIN1 in facilitating gene expression and links phase separation to tumorigenesis, which provides a new perspective for understanding the function of SPIN1.

RNA base editors should ideally be free of immunogenicity, compact, efficient, and specific, which has not been achieved for C > U editing. Here we first describe a compact C > U editor entirely of human origin, created by fusing the human C > U editing enzyme RESCUE-S to Cas inspired RNA targeting system (CIRTS), a tiny, human-originated programmable RNA-binding domain. This editor, CIRTS-RESCUEv1 (V1), was inefficient. Remarkably, a short histidine-rich domain (HRD), which is derived from the internal disordered region (IDR) in the human CYCT1, a protein capable of liquid-liquid phase separation (LLPS), enhanced V1 editing at on-targets as well as off-targets, the latter effect being minor. The V1-HRD fusion protein formed puncta characteristic of LLPS, and various other IDRs (but not an LLPS-impaired mutant) could replace HRD to effectively induce puncta and potentiate V1, suggesting that the diverse domains acted via a common, LLPS-based mechanism. Importantly, the HRD fusion strategy was applicable to various other types of C > U RNA editors. Our study expands the RNA editing toolbox and showcases a general method for stimulating C > U RNA base editors.

Despite their lack of a rigid structure, intrinsically disordered regions (IDRs) in proteins play important roles in cellular functions, including mediating protein-protein interactions. Therefore, it is important to computationally annotate IDRs with high accuracy. In this study, we present Disordered Region prediction using Bidirectional Encoder Representations from Transformers (DR-BERT), a compact protein language model. Unlike most popular tools, DR-BERT is pretrained on unannotated proteins and trained to predict IDRs without relying on explicit evolutionary or biophysical data. Despite this, DR-BERT demonstrates significant improvement over existing methods on the Critical Assessment of protein Intrinsic Disorder (CAID) evaluation dataset and outperforms competitors on two out of four test cases in the CAID 2 dataset, while maintaining competitiveness in the others. This performance is due to the information learned during pretraining and DR-BERT\'s ability to use contextual information.

For a solid understanding of drug characteristics, in vitro measurement of the intrinsic dissolution rate is important. Hydrodynamics are often emphasized as the decisive parameter influencing the dissolution. In this study, experiments and computational fluid dynamic (CFD) simulations showed that the mixing behavior in the rotating disc apparatus causes an inhomogeneous flow field and a systematic error in the calculation of the intrinsic dissolution rate. This error is affected by both the experimental time and the velocity. Due to the rotational movement around the tablet center, commonly utilized in pharmacopeia methods, a broad variance is present with regard to the impact of fluid velocity on individual particles of the specimen surface. As this is significantly reduced in the case of uniform overflow, the flow channel is recommended for investigating the dissolution behavior. It is shown that rotating disc measurements can be compared with flow channel measurements after adjusting the measured data for the rotating disc based on a proposed, representative Reynolds number and a suggested apparatus-dependent correction factor. Additionally, modeling the apparatus-independent intrinsic dissolution rate for different temperatures in the rotating disc apparatus is possible using the adapted Levich\'s equation.

A computational analysis of mass spectrometry data was performed to uncover alternative splicing derived protein variants across chambers of the human heart. Evidence for 216 non-canonical isoforms was apparent in the atrium and the ventricle, including 52 isoforms not documented on SwissProt and recovered using an RNA sequencing derived database. Among non-canonical isoforms, 29 show signs of regulation based on statistically significant preferences in tissue usage, including a ventricular enriched protein isoform of tensin-1 (TNS1) and an atrium-enriched PDZ and LIM Domain 3 (PDLIM3) isoform 2 (PDLIM3-2/ALP-H). Examined variant regions that differ between alternative and canonical isoforms are highly enriched with intrinsically disordered regions. Moreover, over two-thirds of such regions are predicted to function in protein binding and RNA binding. The analysis here lends further credence to the notion that alternative splicing diversifies the proteome by rewiring intrinsically disordered regions, which are increasingly recognized to play important roles in the generation of biological function from protein sequences.

The Heat Shock Protein 90 (Hsp90) molecular chaperone is a key driver of protein homeostasis (proteostasis) under physiologically normal and stress conditions. In eukaryotes, Hsp90 is essential and is one of the most abundant proteins in a cell where the chaperone shuttles between the cytoplasm and nucleus to fold, stabilize, and regulate client proteins and protein complexes. Numerous high-throughput screens have mapped the Hsp90 interactome, building a vast network comprising ∼25% of the proteome in budding yeast. How Hsp90 is able to associate with this diverse and large cadre of targets is critical to comprehending how the proteostatic process works. Here, we review recent progress on our understanding of the molecular underpinnings driving Hsp90-client interactions from both the perspective of the targets and Hsp90. In addition to considering the available Hsp90-client structures, we also assessed recently identified Hsp90-client peptide complexes to build a model that justifies how Hsp90 might recognize a wide spectrum of target proteins. In brief, Hsp90 either directly recognizes a site within an intrinsically disordered region (IDR) of a client protein to transiently regulate that client or it associates with an unstructured polypeptide section created by the concerted efforts of multiple chaperones and cochaperones to stably associate with a client. Overall, Hsp90 exploits a common recognition property (i.e., IDR) within diverse clients to support chaperone-actionthereby enabling its central role in proteostasis.

B lineage priming by pioneer transcription factor EBF1 requires the function of an intrinsically disordered region (IDR). Here, we examine the role of regularly spaced tyrosines in the IDR as potential determinants of IDR function and activity of EBF1. We found that four Y > A mutations in EBF1 reduced the formation of condensates in vitro and subdiffractive clusters in vivo. Notably, Y > A mutant EBF1 was inefficient in promoting B cell differentiation and showed impaired chromatin binding, recruitment of BRG1, and activation of specific target genes. Thus, regularly spaced tyrosines in the IDR contribute to the biophysical and functional properties of EBF1.