Hormonal induction of 3T3-L1 preadipocytes triggers a cascade of events that initiate differentiation into adipocytes. CCAAT/enhancer-binding proteinsβ andδ (C/EBPβ/δ) are expressed early in the differentiation program, but are not immediately active. After a long lag, C/EBPβ/δ become competent to bind to the C/EBP regulatory element in the C/EBPa gene promoter, C/EBPa being a transcriptional activator of numerous adipocyte genes. As C/EBPβ/δ acquire binding activity, they become localized to centromeres as preadipocytes synchronously enter S phase at the onset of mitotic clonal expansion. Localization to centromeres occurs through C/EBP consensus-binding sites in centromeric satellite DNA. C/EBPa, which is antimitotic, becomes centromere-associated much later in the differentiation program as mitotic clonal expansion ceases and the cells become terminally differentiated.