The cover shows a protein plasticity and filament formation of XRCC4 (gold) in complex with ligase IV tandem BRCT domains (red) and with XLF (XRCC4-like factor, green). The article by Hammel et al., pages 32638–32650, describes the combination of crystallography, small angle x-ray scattering, and hydrogen-deuterium exchange mass spectrometry in the characterization of the XRCC4-XLF-DNA complex that permits multiple protein interactions leading to double strand break repair. Article Link (PDF)