Full-length and mutant Helios constructs in MSCV-IRES-GFP retroviral vector. (A) Schematic representation of MSCV-IRES-GFP and 2 Helios constructs. Zinc-finger domains comprising the DNA-binding and multimerization domains of Helios are indicated by the solid boxes. The Helios Δ49-285 variant contained a C-terminal FLAG tag. LTR indicates long terminal repeat; IRES, internal ribosomal entry site; GFP, green fluorescent protein. (B) Coimmunoprecipitation of FLAG-Helios Δ49-285 with HA-IK4. An anti-FLAG monoclonal antibody was used to immunoprecipitate FLAG-Helios Δ49-285 from BOSC23 cell lysates that were transiently transfected with the indicated retroviral constructs. The presence of Helios or Ikaros in the immune complexes was detected by Western blot using anti-Helios or anti-Ikaros polyclonal antibodies.