Binding of Spi-B to the promoter regions of the human PRDM1 and the XBP-1 locus. (A) Schematic representation of the 5′ region of the human PRDM1 and XBP1 locus. Binding sites of primers used for analysis of chromatin immunoprecipitation (ChIP) are indicated relative to the transcription start site. (B-D) ChIP analysis for Spi-B binding. SpiB∼ER-GFP⁺ RAJI cells were cultured in the presence or absence of 4HT for 4 hours and subjected to ChIP using α-ER antibody or, as control, normal rabbit IgG (Ctrl Ig). (B) As positive control for Spi-B binding, precipitated chromatin was analyzed by real-time PCR for abundance of CD40 promoter DNA. The Spi-B open reading frame (ORF) served as irrelevant gene control for Spi-B binding. (C) Precipitated chromatin was analyzed for abundance of 3 different regions (regions a, b, c) of the PRDM1 promoter. (D) Precipitated chromatin was analyzed with primers binding to regions b and locus c upstream of the transcription start in the XBP1 gene. Values are normalized to chromatin levels in control Ig samples. Mean plus or minus SD values of precipitation triplicates are shown. One representative experiment of 2 is shown.