High impact information on Cp18

• Two elements important for amplification of the third chromosome chorion gene cluster, ACE3 and Ori-beta, are directly bound by Orc (origin recognition complex), and two-dimensional gel analysis has revealed that the primary origin used is Ori-beta (refs 7-9) [1].
• To demonstrate that the in vivo localization of DmORC is related to its DNA-binding properties, we find that purified DmORC binds to ACE3 and AER-d in vitro, and like its S. cerevisiae counterpart, this binding is dependent on ATP [2].
• Drosophila ORC specifically binds to ACE3, an origin of DNA replication control element [2].
• However, initiation was nonrandom; the majority of initiations appeared to occur near the Bgl II site located between the s18 and s15 chorion genes [3].
• The role of ACE3 in Drosophila chorion gene amplification [4].

Biological context of Cp18

• One long intergenic sequence, located in the distal 5' flanking region of gene s18, is homologous to ACE3, a major amplification control element and contains an 80-bp A/T-rich sequence, known to stimulate strong binding of the origin recognition complex (ORC) in D. melanogaster [5].
• Therefore ACE3 does not appear to be analogous to a transcription enhancer [4].
• We have characterized at the nucleotide level a 4.8-kilobase pair segment of the third chromosome of Drosophila melanogaster, which contains a cluster of three chorion genes, s18-1, s15-1 and s19-1 [6].
• The highest number of dyad symmetries, reminiscent of sequences that function as viral replication origins, is found associated with the T- and A-rich regions between genes s18-1 and s15-1 [6].
• Here we present the complete nucleotide sequence of this "amplification control element" and of genes encoding the chorion structural proteins s18-1 and s15-1, which are contained within it [7].

Anatomical context of Cp18

• The parent construct supported 18- to 20-fold amplification, and contained the 320 bp ACE3, the approximately 1.2 kb S18 chorion gene and the 840 bp ori-beta [8].
• We have used two types of deletions in the chorion cluster: the first was in vitro generated deletions of the ACE-3 region that were subsequently introduced into the germ line, and the second was deletions induced in vivo within a transposon at a preexisting chromosomal location, thus avoiding the complication of position effects [9].
• Constructs containing chimeric combinations of Drosophila melanogaster and D. grimshawi DNA regions, as well as D. grimshawi sequences alone, can direct expression in the follicular epithelium, in an s18-specific temporal and spatial pattern [10].

Other interactions of Cp18

• Despite marked temporal differences in their accumulation profiles, s36 and s18, putative chorion proteins, were similarly distributed throughout the floor, pillars, and roof of the endochorion [11].
• Using immunolocalization, we observe that ACE3, a 440-bp chorion element that contains information sufficient to drive amplification, directs DmORC localization in follicle cells [2].

References