Gene silencing was first identified in the mating-type system of yeast, but is now recognized to be a general phenomenon in eukaryotic cells. For example, the stable expression patterns of homeotic genes required for proper development in the fruitfly Drosophila depends upon a form of gene silencing. Strikingly, Rap1 also binds to the promoters of many genes, where it functions as an activator of transcription. We are currently trying to understand this process in molecular detail through a combination of genetic and biochemical analysis. Telomere repeat tracts are variable in length, and are synthesized by a specialized reverse transcriptase called telomerase.
All organisms appear to regulate telomere tract length to a species-specific average value.
Significantly, telomere length regulation has been associated in mammalian cells with both aging and cancer. We have recently presented evidence that yeast cells regulate telomere length through a negative feedback mechanism that can discriminate the precise number of Rap1p molecules bound to the repeat tracts. The target of this regulatory system, which may be either telomerase itself of associated proteins, is currently under investigation. Determination of capsid size by satellite bacteriophage P4. DNA flexibility studied by covalent closure of short fragments into circles.