Proximity-based proteomic profiling uncovers distinct interactome of human RAG1 and RAG2.

The recombination-activating gene (RAG) complex initiates adaptive immunity by catalyzing V(D)J recombination to generate diverse antigen receptors. While the catalytic function of the RAG core is well defined, its regulatory interactions and physiological roles remain poorly understood due to limited knowledge of RAG-associated proteins. The RAG complex forms a heterotetramer of two RAG1 and RAG2 subunits, yet the individual contributions of each subunit remain unclear. Here, we use TurboID-mediated proximity labelling to map the human RAG interactome. By fusing TurboID to RAG1 or RAG2, we identify 88 RAG1- and 146 RAG2-associated proteins, with only 23 shared proteins, indicating distinct sets of proximal proteins. Although RAG1 and RAG2 are thought to exert their physiological functions by forming a complex, they display distinct potential interaction networks, suggesting subunit-specific functions and revealing their spatial proximity to each subunit. These findings uncover distinct RAG1 and RAG2 interaction landscapes and establish a framework for exploring broader RAG functions in immunity.