KLF5 binds Dβ1 promoter in vitro and in vivo. (A) KLF5 and Sp1 are among nuclear proteins in pro-T cells binding the -35 motif in the Dβ1 promoter. Nuclear extracts from p5424 cells were incubated with no antibody, anti-Sp1 antiserum, anti-KLF5 antiserum, or control antiserum at room temperature for 20 minutes before EMSA. (B) KLF5 binds the Dβ1 promoter in p5424 cells in vivo. p5424 and A20 cells were cross-linked by 1% formaldehyde, sonicated, and subjected to chromatin immunoprecipitation assay with anti-KLF5 antiserum, anti-Sp1 antiserum, control antiserum, or without antibody. Immunoprecipitates were assayed for Dβ1 or IgH DQ52 promoter sequences using nested PCR.