Copy number and orientation determine the susceptibility of a gene to silencing by nearby heterochromatin in Drosophila

The classical phenomenon of position-effect variegation (PEV) is the mosaic expression that occurs when a chromosomal rearrangement moves a euchromatic gene near heterochromatin. A striking feature of this phenomenon is that genes far away from the junction with heterochromatin can be affected, as i...

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Bibliographic Details
Published in:Genetics (Austin) 1996-02, Vol.142 (2), p.447-458
Main Authors: Sabl, J.F, Henikoff, S
Format: Article
Language:English
Subjects:
alleles
Animals
Biochemistry
brown gene
color
compound eyes
Drosophila melanogaster
Drosophila melanogaster - genetics
Female
Gene Dosage
gene expression
Gene Expression Regulation
gene silencing
Genes, Insect
genetic markers
genetic regulation
Genetics
Heterochromatin
Insects
Investigations
Male
Multigene Family
mutagenesis
phenotype
position effect
transcription (genetics)
Transgenes
transgenic animals
variegation
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Summary:The classical phenomenon of position-effect variegation (PEV) is the mosaic expression that occurs when a chromosomal rearrangement moves a euchromatic gene near heterochromatin. A striking feature of this phenomenon is that genes far away from the junction with heterochromatin can be affected, as if the heterochromatic state "spreads." We have investigated classical PEV of a Drosophila brown transgene affected by a heterochromatic junction approximately 60 kb away. PEV was enhanced when the transgene was locally duplicated using P transposase. Successive rounds of P transposase mutagenesis and phenotypic selection produced a series of PEV alleles with differences in phenotype that depended on transgene copy number and orientation. As for other examples of classical PEV, nearby heterochromatin was required for gene silencing. Modifications of classical PEV by alterations at a single site are unexpected, and these observations contradict models for spreading that invoke propagation of heterochromatin along the chromosome. Rather, our results support a model in which local alterations affect the affinity of a gene region for nearby heterochromatin via homology-based pairing, suggesting an alternative explanation for this 65-year-old phenomenon.
ISSN:0016-6731
1943-2631
1943-2631
DOI:10.1093/genetics/142.2.447