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Mol. Cell. Biol., 10 1997, 6157-6166, Vol 17, No. 10
S Strehl, JM LaSalle and M Lalande
Establishing how mammalian chromosome replication is regulated and how
groups of replication origins are organized into replication bands will
significantly increase our understanding of chromosome organization.
Replication time bands in mammalian chromosomes show overall congruency
with structural R- and G-banding patterns as revealed by different
chromosome banding techniques. Thus, chromosome bands reflect variations in
the longitudinal structure and function of the chromosome, but little is
known about the structural basis of the metaphase chromosome banding
pattern. At the microscopic level, both structural R and G bands and
replication bands occupy discrete domains along chromosomes, suggesting
separation by distinct boundaries. The purpose of this study was to
determine replication timing differences encompassing a boundary between
differentially replicating chromosomal bands. Using competitive PCR on
replicated DNA from flow-sorted cell cycle fractions, we have analyzed the
replication timing of markers spanning roughly 5 Mb of human chromosome
13q14.3/q21.1. This is only the second report of high-resolution analysis
of replication timing differences across an R/G-band boundary. In contrast
to previous work, however, we find that band boundaries are defined by a
gradient in replication timing rather than by a sharp boundary separating R
and G bands into functionally distinct chromatin compartments. These
findings indicate that topographical band boundaries are not defined by
specific sequences or structures.
Copyright © 1997, American Society for Microbiology
High-resolution analysis of DNA replication domain organization across an R/G-band boundary
Genetics Division, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
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