Add time:08/12/2019         Source:sciencedirect.com

Publisher SummaryThis chapter discusses the position-effect variegation—an assay for nonhistone chromosomal proteins and chromatin assembly and modifying factors. The extensive analyses of the homeotic genes in Drosophila suggest that chromatin structure plays a fundamental role in the control of segment determination and differentiation. Hence, chromatin structure plays an important role in the regulation of gene expression. The formation of transcriptionally competent domains is an essential first step in proper gene expression. The phenomenon of position-effect variegation (PEV) resembles X-inactivation in mammals. It may serve as a suitable assay system for the recovery of mutations in nonhistone chromosomal proteins (NHCPs). PEV is the mosaic expression of a gene, associated with a chromosomal or genomic rearrangement. In most instances, PEV occurs when a gene, normally located in euchromatin, is placed adjacent to a broken segment of heterochromatin. The variegating gene is inactivated in some cells but remains transcriptionally competent in other cells, giving a mosaic phenotype. PEV has been most extensively studied in Drosophila, but it has also been described in vertebrates, lower eukaryotes, and plants to a broken segment of heterochromatin. The two most extensively characterized affecters of PEV are temperature and the number of Y chromosomes in the genome.

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