Delineation of DNA replication time zones by fluorescence in situ hybridization
Selig, S.; Okumura, K.; Ward, D.C.; Cedar, H.
EMBO Journal 11(3): 1217-1225
1992
ISSN/ISBN: 0261-4189 PMID: 1547781 Document Number: 404971
Fluorescence in situ hybridization has been used to visualize specific genomic DNA sequences in interphase nuclei. In normal diploid cells, unreplicated DNA segments give singlet hybridization signals while replicated loci are characterized by doublets. The distribution of these two patterns in unsynchronized cell populations can be used to determine the S phase replication time of any DNA sequence. The validity of this approach was established by analyzing genes whose replication profiles in expressing and non-expressing cells had been determined previously by conventional methods. Using this technique it has been possible to map the replication timing topography of the DNA within and flanking the cystic fibrosis (CF) gene locus on chromosome 7. The gene itself is located within a defined time zone which is approximately 500 kb in length and is under developmental control. It is early replicating in cells which express CF but late replicating in other cell types. These time zones probably represent basic units of chromosome structure.