The cyclin B1 gene is actively transcribed during mitosis in HeLa cells

In mammalian cells, the expression level of the cyclin B1 gene plays a crit ical role in the progression through mitosis. Here we demonstrate that the transcriptional activity of the human cyclin B1 promoter, as well as the ra te of gene transcription, is high during mitosis. Indeed, the cyclin B1 pro moter maintains an open chromatin configuration at the mitotic stage. Consi stent with this, we show that the cyclin B1 promoter is occupied and bound to NF-Y during mitosis in vivo. Our results provide the first example of RN A polymerase II-dependent transcription during mitosis in mammalian cells.