Delayed replication timing leads to delayed mitotic chromosome condensation and chromosomal instability of chromosome translocations.

Chromosomal rearrangements are found in virtually all types of human cancers. We show that certain chromosome translocations display a delay in mitotic chromosome condensation that is associated with a delay in the mitosis-specific phosphorylation of histone H3. This delay in mitotic condensation is preceded by a delay in both the initiation as well as the completion of chromosome replication. In addition, chromosomes with this phenotype participate in numerous secondary translocations and rearrangements. Chromosomes with this phenotype were detected in five of seven tumor-derived cell lines and in five of thirteen primary tumor samples. These data suggest that certain chromosomal rearrangements found in tumor cells cause a significant delay in replication timing of the entire chromosome that subsequently results in delayed mitotic chromosome condensation and ultimately in chromosomal instability.