Photocatalytic proximity labeling of HEK293FT cells nuclear extract proteins interacting with G-quadruplex DNA was performed and the labeled proteins were identified using an LC-nano-ESI-MS comprising a quadrupole time-of-flight mass spectrometer equipped with a nanospray ion source and nanoLC system. The trap column used for nanoLC was a NanoLC Trap ChromXP C18, and the separation column was a capillary column packed with 3 μm C18-silica particles.