PAX5-JAK2 is able to bind and regulate PAX5 target genes. (A) Schematic representation of the PAX5-JAK2 fusion protein, PAX5, and JAK2. PD, paired DNA-binding domain; OP, octapeptide; HD, partial homeodomain; TA, transactivation domain; I, inhibitory domain; JH1, kinase domain; JH2, pseudokinase domain; JH3-4, SH2-like domain; JH6-7, FERM domain; arrows indicate nuclear localization signals. (B) Chromatin immunoprecipitation followed by quantitative real-time PCR analysis of NALM-6 cells carrying a luciferase vector (luc) or expressing V5-tagged PAX5, a DNA-binding deficient mutant thereof (V5-PAX5-K67/87/89A), or V5-PAX5-JAK2. The amount of DNA precipitated with V5 antibody was determined by quantitative PCR using PAX5 target loci-specific primers and normalized to input DNA. The results of 1 of 3 representative experiments are shown. 3′, 3-prime region; TSS, transcription start site; I, intron; E, exon. (C-D) Reporter gene assays in HEK293 cells transfected with (C) luc-CD19 or (D) pGL4-CD79A-TSS luciferase reporter and indicated V5-tagged expression vectors. Firefly was normalized to Renilla luciferase activity and to the empty luciferase vector and the expression vector control. The bars represent the means ± SD of ≥3 independent experiments each performed in triplicate. Significance levels were determined using an unpaired 2-tailed Student t test comparing the mean fold activation values of 3 independent experiments with the hypothetical value of 1 (*P < .05, **P < .01, ***P < .001).