Position effect variegation in yeast.
Classically, position effect variegation has been studied in Drosophila and results when a euchromatic gene is placed adjacent to either centromeric heterochromatin or to a telomeric domain. In such a circumstance expression of the locus variegates, being active in some cells and silent in others. Over the last few years a comparable phenomenon in yeast has been discovered. This system promises to tell us much about this curious behavior. Indeed, experiments reported recently(1) indicate that the variegation of a yeast telomeric gene is cell-cycle regulated. The results suggest the following model. During DNA replication there is a disassembly of chromatin that allows a competition between silencing factors and transactivators to take place. Thus, reassembly of the domain may result in either the repression or the expression of the affected gene and, hence, produce a variegating phenotype.
Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA 19111.
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D000818:Animals; D002453:Cell Cycle; D015825:Chromosomes, Fungal; D004330:Drosophila / Q000235:genetics; D005800:Genes, Fungal; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics*; D012568:Schizosaccharomyces / Q000166:cytology / Q000235:genetics*; D016615:Telomere / Q000648:ultrastructure