DISPLACEMENT OF SEQUENCE-SPECIFIC TRANSCRIPTION FACTORS FROM MITOTIC CHROMATIN

The general inhibition in transcriptional activity during mitosis abol ishes the stress-inducible expression of the human hsp70 gene. Among t he four transcription factors that bind to the human hsp70 promoter, t he DNA-binding activities of three (C/EBP, GBF, and HSF1) were normal, while Sp1 showed reduced binding activity in mitotic cell extracts. I n vivo footprinting and immunocytochemical analyses revealed that all of the sequence-specific transcription factors were displaced from pro moter sequences as well as from bulk chromatin during mitosis. The cor relation of transcription factor displacement with chromatin condensat ion suggests an involvement of chromatin structure in mitotic repressi on. However, retention of DNase I hypersensitivity suggests that the h sp70 promoter was not organized in a canonical nucleosome structure in mitotic chromatin. Displacement of transcription factors from mitotic chromosomes could present another window in the cell cycle for resett ing transcriptional programs.