Replication timing, chromosomal bands, and isochores

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 105; no. 9; pp. 3433 - 3437
• Main Authors: Costantini, Maria, Bernardi, Giorgio
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 04.03.2008; National Acad Sciences
• Subjects: Base Composition; Biological Sciences; Cell cycle; Chromosome Banding; Chromosomes; Chromosomes, Human - genetics; Chromosomes, Human, Pair 11; Chromosomes, Human, Pair 21; Chromosomes, Human, Pair 6; DNA Replication Timing - genetics; Eukaryotes; Genomes; Genomics; Globular star clusters; High resolution; Human chromosomes; Human genome; Humans; Isochores; Isochores - genetics; Replication origin; Replicon; Vertebrates
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0710587105

Chromosome replication timing is biphasic (early-late) in the cell cycle of vertebrates and of most (possibly all) eukaryotes. In the present work we have compared the extended, detailed replication timing maps that are available, namely those of human chromosomes 6, 11q, and 21q, with chromosomal bands as visualized at low (400 bands), high (850 bands), and highest (3,200 isochores) resolution. We have observed that the replicons located in a given isochore practically always show either all early or all late replication timing and that early-replicating isochores are short and GC-rich and late-replicating isochores are long and GC-poor. In the vast majority of cases, replicons are clustered in isochores, which are themselves most often clustered in early- or late-replication timing zones and may often reach the size of high-resolution bands and, very rarely, even that of low-resolution bands. Finally, we show that our results should be representative for the whole human genome and thus help to predict replication timing zones in all chromosomes.