TCL1 acts as a selective non-covalent inhibitor targeting the Pru domain of the Rpn-13 subunit within the 19S regulatory particle (19S RP) of the proteasome, with an IC50 value around 26 μM. It disrupts the recognition and transport of ubiquitinated proteins by Rpn-13, thus inhibiting proteasomal degradation and affecting intracellular protein metabolism balance. TCL1 holds potential for research in hematologic malignancies.