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Mol. Cell. Biol., Oct 1997, 6167-6174, Vol 17, No. 10
JS Michaelson, O Ermakova, BK Birshtein, N Ashouian, C Chevillard, R Riblet and CL Schildkraut
DNA replication in mammalian cells is a precisely controlled physical and
temporal process, likely involving cis-acting elements that control the
region(s) from which replication initiates. In B cells, previous studies
showed replication timing to be early throughout the immunoglobulin heavy
chain (Igh) locus. The implication from replication timing studies in the
B-cell line MPC11 was that early replication of the Igh locus was regulated
by sequences downstream of the C alpha gene. A potential candidate for
these replication control sequences was the 3' regulatory region of the Igh
locus. Our results demonstrate, however, that the Igh locus maintains early
replication in a B-cell line in which the 3' regulatory region has been
deleted from one allele, thus indicating that replication timing of the
locus is independent of this region. In non-B cells (murine erythroleukemia
cells [MEL]), previous studies of segments within the mouse Igh locus
demonstrated that DNA replication likely initiated downstream of the Igh
gene cluster. Here we use recently cloned DNA to demonstrate that segments
located sequentially downstream of the Igh 3' regulatory region continue to
replicate progressively earlier in S phase in MEL. Furthermore, analysis by
two-dimensional gel electrophoresis indicates that replication forks
proceed exclusively in the 3'-to-5' direction through the region 3' of the
Igh locus. Extrapolation from these data predicts that initiation of DNA
replication occurs in MEL at one or more sites within a 90-kb interval
located between 40 and 130 kb downstream of the 3' regulatory region.
Copyright © 1997, American Society for Microbiology
Regulation of the replication of the murine immunoglobulin heavy chain gene locus: evaluation of the role of the 3' regulatory region
Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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