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© The Rockefeller University Press,
0021-9525/2001//101 $5.00
The Journal of Cell Biology, Volume 153, Number 1,
, 2001 101-110
Original Article |
Centromeres Are Specialized Replication Domains in Heterochromatin
steveh{at}fhcrc.org
The properties that define centromeres in complex eukaryotes are poorly understood because the underlying DNA is normally repetitive and indistinguishable from surrounding noncentromeric sequences. However, centromeric chromatin contains variant H3-like histones that may specify centromeric regions. Nucleosomes are normally assembled during DNA replication; therefore, we examined replication and chromatin assembly at centromeres in Drosophila cells. DNA in pericentric heterochromatin replicates late in S phase, and so centromeres are also thought to replicate late. In contrast to expectation, we show that centromeres replicate as isolated domains early in S phase. These domains do not appear to assemble conventional H3-containing nucleosomes, and deposition of the Cid centromeric H3-like variant proceeds by a replication-independent pathway. We suggest that late-replicating pericentric heterochromatin helps to maintain embedded centromeres by blocking conventional nucleosome assembly early in S phase, thereby allowing the deposition of centromeric histones.
Key Words: centromere • heterochromatin • DNA replication • histone • Drosophila
© 2001 The Rockefeller University Press
Abbreviations used in this paper: Bio, biotin; dig, digoxigenin; GFP, green fluorescent protein.
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