Histone readers MLLT1 and MLLT3 concentrate AID to confer locus specificity.

Loss of histone readers MLLT1 and MLLT3 eliminates all AID-dependent mutagenic activity, highlighting their essential role in locus-specific antibody diversification.

• Why it matters: Understanding how AID selectively targets immunoglobulin loci is crucial because off-target activity can lead to B cell lymphoma, yet the mechanisms of its locus specificity remain unclear.
• What they did: The study used genetic deletion and fusion approaches to show that MLLT1 and MLLT3 bind to AID and enrich it downstream of promoters, with their combined loss abolishing mutagenesis in mouse and human B cells.
• The result: Findings demonstrate that MLLT1 and MLLT3 create condensates that spatially confine AID activity, enabling precise targeting and enabling potential therapeutic strategies to control off-target mutagenesis.