TOPORS-mediated RAD51 SUMOylation facilitates homologous recombination repair.

Homologous recombination (HR) is critical for error-free repair of DNA double-strand breaks. Chromatin loading of RAD51, a key protein that mediates the recombination, is a crucial step in the execution of the HR repair. Here, we present evidence that SUMOylation of RAD51 is crucial for the RAD51 recruitment to chromatin and HR repair. We found that topoisomerase 1-binding arginine/serine-rich protein (TOPORS) induces the SUMOylation of RAD51 at lysine residues 57 and 70 in response to DNA damaging agents. The SUMOylation was facilitated by an ATM-induced phosphorylation of TOPORS at threonine 515 upon DNA damage. Knockdown of TOPORS or expression of SUMOylation-deficient RAD51 mutants caused reduction in supporting normal RAD51 functions during the HR repair, suggesting the physiological importance of the modification. We found that the SUMOylation-deficient RAD51 reduces the association with its crucial binding partner BRCA2, explaining its deficiency in supporting the HR repair. These findings altogether demonstrate a crucial role for TOPORS-mediated RAD51 SUMOylation in promoting HR repair and genomic maintenance.

Scattering Elimination of Heterodyne-Detected Two-Dimensional Infrared Spectra Using Choppers and Shutters.

Obtaining high-quality 2D IR spectra of heterogeneous samples such as perovskite films or metal-organic framework powder is hampered by severe light scattering. In the pump-probe (PP) method, this problem can be circumvented by phase cycling. However, in the heterodyned photon echo (HPE) method, phase cycling does not function as effectively as the PP method. This study demonstrates that the scattering problem can be solved mechanically by introducing another chopper and two shutters into the existing 2D IR setup without moving any translation stages to introduce a phase shift in the HPE method. For a perovskite film having a very rough surface, containing a small amount of residual dimethylformamide, and having a maximum absorbance of ∼0.0004 in the C═O stretch region, this advanced experimental method is tested and proven to be highly effective.

Interconverting Hydrogen-Bonding and Weak n → π* Interactions in Aqueous Solution: A Direct Spectroscopic Evidence.

Molecular structure and function depend on myriad noncovalent interactions. However, the weak and transient nature of noncovalent interactions in solution makes them challenging to study. Information on weak interactions is typically derived from theory and indirect structural data. Solvent fluctuations, not revealed by structure analysis, further complicate the study of these interactions. Using 2D infrared spectroscopy, we show that the strong hydrogen bond and the weak n → π* interaction coexist and interconvert in aqueous solution. We found that the kinetics of these interconverting interactions becomes faster with increasing water content. This experimental observation provides a new perspective on the existence of weak noncovalent interactions in aqueous solution.