The genomic silencing of position-effect variegation in Drosophila melanogaster: interaction between the heterochromatin-associated proteins Su(var)3-7 and HP1.
Position-effect variegation results from mosaic silencing by chromosomal rearrangements juxtaposing euchromatin genes next to pericentric heterochromatin. An increase in the amounts of the heterochromatin-associated Su(var)3-7 and HP1 proteins augments silencing. Using the yeast two-hybrid protein interaction trap system, we have isolated HP1 using Su(var)3-7 as a bait. We have then delimited three binding sites on Su(var)3-7 for HP1. On HP1, the C-terminal moiety, including the chromo shadow domain, is required for interaction. In vivo, both proteins co-localise not only in heterochromatin, but also in a limited set of sites in euchromatin and at telomeres. When delocalised to the sites bound by the protein Polycomb in euchromatin, HP1 recruits Su(var)3-7. Finally, and in contrast with euchromatin genes, a decrease in the amounts of both proteins enhances variegation of the light gene, one of the few genetic loci mapped within pericentric heterochromatin. This body of data supports a direct link between Su(var)3-7 and HP1 in the genomic silencing of position-effect variegation.
Delattre
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Department of Zoology and Animal Biology, University of Geneva, CH-1211 Geneva 4, Switzerland. pierre.spierer@zoo.unige.ch.
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Tonka
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D000483:Alleles; D000818:Animals; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D004276:DNA, Satellite / Q000235:genetics; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics*; D022041:Euchromatin / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000235:genetics; D015321:Gene Rearrangement / Q000502:physiology; D020868:Gene Silencing; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism*; D016254:Mutagenesis, Insertional / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D002868:Chromosomal Proteins, Non-Histone; D004276:DNA, Satellite; D029721:Drosophila Proteins; D022041:Euchromatin; D006570:Heterochromatin; D012097:Repressor Proteins; C089148:Su(var)3-9 protein, Drosophila; D000090266:Chromobox Protein Homolog 5