Molecular and Cellular Biology, January 1999, p. 547-555, Vol. 19, No. 1
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
-dE2F Locus of Drosophila
melanogaster

Mitsubishi Kasei Institute of Life Sciences,
Received 13 July 1998/Returned for modification 17 September
1998/Accepted 19 October 1998
In the early stage of Drosophila embryogenesis, DNA
replication initiates at unspecified sites in the chromosome. In
contrast, DNA replication initiates in specified regions in cultured
cells. We investigated when and where the initiation regions are
specified during embryogenesis and compared them with those observed in cultured cells by two-dimensional gel methods. In the DNA polymerase
gene (DNApol
) locus, where an initiation region,
oriD
, had been identified in cultured Kc cells,
repression of origin activity in the coding region was detected after
formation of cellular blastoderms, and the range of the initiation
region had become confined by 5 h after fertilization. During this
work we identified other initiation regions between oriD
and the Drosophila E2F gene (dE2F) downstream
of DNApol
. At least four initiation regions showing
replication bubbles were identified in the 65-kb
DNApol
-dE2F locus in 5-h embryos, but only two were
observed in Kc cells. These results suggest that the specification
levels of origin usage in 5-h embryos are in the intermediate state
compared to those in more differentiated cells. Further, we found a
spatial correlation between the active promoter regions for
dE2F and the active initiation zones of replication. In 5-h
embryos, two known transcripts differing in their first exons were
expressed, and two regions close to the respective promoter regions for
both transcripts functioned as replication origins. In Kc cells, only one transcript was expressed and functional replication origins were
observed only in the region including the promoter region for this transcript.
*
Corresponding author. Mailing address: Mitsubishi Kasei
Institute of Life Sciences, 11 Minami-oya, Machida, Tokyo 194-8511, Japan. Phone: 81-427-24-6251. Fax: 81-427-24-6317. E-mail:
tomo{at}libra.ls.m-kagaku.co.jp.
Present address: Horikoshi Gene Selector Project, ERATO, JST,
Tsukuba, Ibaraki 300-2635, Japan.
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