VERY LATE DNA-REPLICATION IN THE HUMAN CELL-CYCLE

G(2) was defined originally as the temporal gap between the terminatio n of DNA replication and the beginning of mitosis. In human cells, the G(2) period was estimated to be 3-4 h, However, the absence of replic ative DNA synthesis during this period designated G(2) has never been shown conclusively, In this report, we show that, at some autosomal an d X linked loci, programmed DNA replication continues within 90 min of mitosis, Furthermore, the major accumulation of cyclin B1, a cell-cyc le marker that is usually ascribed to G(2) overlaps extensively with v ery late DNA replication. We conclude that the G(2) period is much sho rter than previously thought and may, in some cells, be nonexistent.