The arginine methyltransferase PRMT5 directly interacts with BCL6. (A) Co-IP experiments for PRMT5 and BCL6 in 293T cells transfected with BCL6. (B) Co-IP experiments for PRMT5 and BCL6 in SUDHL8 and U2932 DLBCL cell lines. (C) PRMT5 and BCL6 interact in normal CD77⁺ GC B cells, enriched as described in supplemental Materials and methods. (D) GST pull-down assay of recombinant GST-PRMT5 and BCL6-MYC/DDK proteins. Purified GST-PRMT5 or GST proteins were incubated with BCL6-MYC/DDK protein for 12 hours. The coprecipitated BCL6 and PRMT5 proteins were detected by western blot with anti-GST and anti-BCL6 antibodies.