ChIP assays of RNA Pol II binding to the cyclin D1 promoter and IgH regulatory regions. (A) Pol II bound to the cyclin D1 promoter in the cyclin D1⁺ MCL cell lines Granta (G), NCEB-1 (N). Pol II also bound to IgH regulatory regions (Eμ, HS4, HS3) in Granta, NCEB-1, and Manca (M) cells, which contain chromosomal translocation involving IgH regulatory elements. Myeloid HL60 cells were used as a negative control. (B) MCF7, a cyclin D1⁺ breast cancer cell line, demonstrated Pol II binding in the cyclin D1 promoter region but not the IgH regulatory elements. EBV-immortalized human B cells, LCL1 and LCL2, showed Pol II binding in the Eμ intronic enhancer region. K562 was used as a negative control. (C) Normal human CD4⁺ T cells (NT) and activated T-cell clone (D160) showed no Pol II binding in either region. Granta (G) and NCEB-1 (N) were used as positive controls.