Reference Report

Reference
Citation	Pflumm, M.F., Botchan, M.R. (2001). Orc mutants arrest in metaphase with abnormally condensed chromosomes. Development 128(9): 1697--1707. (Export to RIS)
FlyBase ID	FBrf0135731
Publication Type	Research paper
PubMed ID	11290306
PubMed Abstract	The origin recognition complex (ORC) is a six subunit complex required for eukaryotic DNA replication initiation and for silencing of the heterochromatic mating type loci in Saccharomyces cerevisiae. Our discovery of the Drosophila ORC complex concentrated in the centric heterochromatin of mitotic cells in the early embryo and its interactions with heterochromatin protein 1 (HP-1) lead us to speculate that ORC may play some general role in chromosomal folding. To explore the role of ORC in chromosomal condensation, we have identified a mutant of subunit 5 of the Drosophila melanogaster origin recognition complex (Orc5) and have characterized the phenotypes of both the Orc5 and the previously identified Orc2 mutant, k43. Both Orc mutants died at late larval stages and surprisingly, despite a reduced number of S-phase cells, an increased fraction of cells were also detected in mitosis. For this latter population of cells, Orc mutants arrest in a defective metaphase with shorter and thicker chromosomes that fail to align at the metaphase plate within a poorly assembled mitotic spindle. In addition, sister chromatid cohesion was frequently lost. PCNA and MCM4 mutants had similar phenotypes to Orc mutants. We propose that DNA replication defects trigger the mitotic arrest, due to the fact that frequent fragmentation was observed. Thus, cells have a mitotic checkpoint that senses chromosome integrity. These studies also suggest that the density of functional replication origins and completion of S phase are requirements for proper chromosomal condensation.
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Language of Publication	English
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Publication Type	Journal
Abbreviation	Development
Title	Development
Publication Year	1987-
ISBN/ISSN	0950-1991
Data from Reference
Aberrations (6)
	Df(2L)b84a9 Df(2L)TE35B-203 Df(3R)293γ7 Dp(2;3)17 In(2L)b79h1A In(2LR)b81a2
Alleles (15)
	Arpc1¹ dpa¹ lat^lE344 lat^vr6.35 mus209⁰²⁴⁴⁸ Orc2¹ Orc2² Orc2^unspecified Orc2^γ4 Orc5¹ Orc5² Orc5^+tPa Orc5^unspecified Orc5^Δ w^+mW.hs
Constructs (2)
	P{Orc5^+tPa} P{Orc5^Δ}
Genes (12)
	Arpc1 b DNApol-γ35 dpa His3 lat mus209 Orc2 Orc5 Sos tam w
Insertions (4)
	P{Orc5^+tPa}24 P{Orc5^+tPa}33 P{Orc5^+tPa}312 P{Orc5^Δ}12