Our earlier results have shown that polyamine depletion affected DNA replication negatively, presumably by reducing the rate of DNA elongation. The G1 to S transition and the G2 phase progression were affected only after several cell cycles. The number and the spatial distribution of replication domains vary in a specific pattern throughout the S phase. Using confocal laser scanning microscopy, we found that neither the number of replication domains nor their spatial distribution was affected in polyamine-depleted cells. This would have been the case if DNA replication initiation was affected.
Further work is needed to establish whether the polyamines have a specific role in DNA replication.
DNA replication requires the presence of a number of proteins which have a direct or indirect role for the incorporation of the nucleotides into DNA as well as for the structural integrity of the chromatin. Topoisomerases are required to release various stresses in DNA that might affect the progress of the replication machinery. Using a decatenation assay, we have found that the topoisomerase II activity in cell extracts is the same in control and polyamine-depleted cells. However, when using the single cell gel electrophoresis assay to study the actual efficiency of topoisomerase II in situ, we found that the enzyme was less active in polyamine-depleted cells than in control cells. These results imply that there are conformational restraints on the DNA of polyamine-depleted cells, a notion suggested by other studies as well.