Compartmentalization by liquid-liquid phase separation is implicated in transcription. It remains unclear whether and how transcriptional condensates accelerate the search of transcriptional regulatory factors for their target sites. Furthermore, the molecular mechanisms by which regulatory factors nucleate on chromatin to assemble transcriptional condensates remain incompletely understood. The CBX-PRC1 complexes compartmentalize key developmental regulators for repression through phase-separated condensates driven by the chromobox 2 (CBX2) protein. Here, by using live-cell single-molecule imaging, we show that CBX2 nucleates on chromatin independently of H3K27me3 and CBX-PRC1. The interactions between CBX2 and DNA are essential for nucleating CBX-PRC1 on chromatin to assemble condensates. The assembled condensates shorten 3D diffusion time and reduce trials for finding specific sites through revisiting the same or adjacent sites repetitively, thereby accelerating CBX2 in searching for target sites. Overall, our data suggest a generic mechanism by which transcriptional regulatory factors nucleate to assemble condensates that accelerate their target-search process.

A metal-free synthesis of biaryl compounds was achieved under photo-irradiation, which represents a milder alternative for cross-coupling reactions.

Many charge-transporting molecular systems function as ordered or disordered arrays of solid state materials composed of nonpolar (or weakly polar) molecules. Due to low dielectric constants for nonpolar systems, it is common to ignore the effects of outer-shell reorganization energy (λ_out). However, ignoring λ_out has not been properly supported and it can severely impact predictions and insights derived. Here, we estimate λ_out by two means: from experimental ultraviolet photoelectron spectra, in which vibronic progression in these spectra can be fitted with the widths of peaks determining the low-frequency component in reorganization energy, regarded to be closely associated with λ_out, and from molecular dynamic (MD) simulation of nonpolar molecules, in which disorder or fluctuation statistics for energies of charged molecules are calculated. An upper bound for λ_out was obtained as 505 and 549 meV for crystalline anthracene (140 K) and pentacene (50 K), respectively, by fitting of experimental data, and 212 and 170 meV, respectively, from MD simulations. These values are comparable to the inner-sphere reorganization energy (λ_in) arising from intramolecular vibration. With corresponding spectral density functions calculated, we found that λ_out is influenced both by low- and high-frequency dynamics, in which the former arises from constrained translational and rotational motions of surrounding molecules. In an amorphous state, about half of the λ_out's obtained are from high-frequency components, which is quite different from the conventional polar solvation. Moreover, crystalline systems exhibit super-Ohmic spectral density, whereas amorphous systems are sub-Ohmic.