Density transfer as a method to analyze the progression of DNA replication forks.

The density transfer technique is a valuable tool to examine the progression of individual DNA replication forks. It is based on the transfer of cells from a medium containing dense isotopes to a medium with light (normal) isotopes (or vice versa), to obtain DNA sequences hybrid in density that can be identified as replicated molecules. Using specific DNA probes along a chromosome, the dense isotope transfer method allows determining the extent of replication at any position of a replicon and the rate of replication fork progression. In the eukaryotic model budding yeast, this technique has been useful to establish a role for different proteins during the elongation of chromosomal replication and to analyze the movement and stability of DNA replication forks under different experimental conditions.