(A) ChIP on DNA promoter microarrays (ChIP on chip). 32D/G-GSF–R-C/EBPα-ER cells or ER-expressing cells were treated with E₂ for 4 hours. The diagram shows an amplified view of the Cebpg locus in chromosome 7. Genes (including Cebpg) are indicated in green, either on the plus or on the minus strand. Specific hybridization was observed (multiple probes in blue) to the representative Cebpg promoter region (– strand), whereas almost none of the other loci in that region appeared to be enriched by ChIP. (B) C/EBPα represses CEBPG promoter–driven luciferase activity. 293T cells, which endogenously express C/EBPγ, were cotransfected with 100 ng CEBPG luciferase reporter vector (–354 to +1) and increasing amounts of a C/EBPα expression plasmid, encoding for either the p42 or p30 form. (C) Mutation of the C/EBP-binding sites in the CEBPG luciferase reporter vector does not affect C/EBPα repression. 100 ng of the mutated reporter vector were cotransfected with increasing amounts of p42 C/EBPα plasmid. (D) C/EBPα suppresses CEBPG promoter activity of a short CEBPG reporter construct. 100 ng of a reporter construct containing 3 E2F-binding sites were cotransfected with different amounts of C/EBPα expression plasmid. (E) C/EBPα reduces E2F1 transactivation of the C/EBPγ promoter. 100 ng of the short C/EBPγ reporter construct was cotransfected with 100 ng E2F1 expression construct and increasing amounts of C/EBPα expression plasmid. The y axis indicates the relative percentage of luciferase activity. Results represent the average of at least 3 independent experiments; bars indicate SD.