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DNA topology, not DNA sequence, is a critical determinant for Drosophila ORC–DNA binding
Author(s) -
Remus Dirk,
Beall Eileen L,
Botchan Michael R
Publication year - 2004
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1038/sj.emboj.7600077
Subject(s) - biology , dna , dna supercoil , hmg box , in vitro recombination , genetics , dna replication , dna sequencing , gene , dna binding site , microbiology and biotechnology , dna binding protein , peptide sequence , molecular cloning , transcription factor , gene expression , promoter
Drosophila origin recognition complex (ORC) localizes to defined positions on chromosomes, and in follicle cells the chorion gene amplification loci are well‐studied examples. However, the mechanism of specific localization is not known. We have studied the DNA binding of DmORC to investigate the cis ‐requirements for DmORC:DNA interaction. DmORC displays at best six‐fold differences in the relative affinities to DNA from the third chorion locus and to random fragments in vitro , and chemical probing and DNase1 protection experiments did not identify a discrete binding site for DmORC on any of these fragments. The intrinsic DNA‐binding specificity of DmORC is therefore insufficient to target DmORC to origins of replication in vivo . However, the topological state of the DNA significantly influences the affinity of DmORC to DNA. We found that the affinity of DmORC for negatively supercoiled DNA is about 30‐fold higher than for either relaxed or linear DNA. These data provide biochemical evidence for the notion that origin specification in metazoa likely involves mechanisms other than simple replicator–initiator interactions and that in vivo other proteins must determine ORC's localization.