Differential nuclear localization does not determine the silencing status of Saccharomyces cerevisiae telomeres

In saccharomyces cerevisiae, genes near telomeres are transcriptionally repressed, a phenomenon termed telomere position effect. (TPE). Yeast. telomeres cluster near the nuclear periphery, as do foci of proteins essential for TPE: Rap1p, Sir2-4p, and yKu70p/yKu80p. However, it is not clear if localization of telomeres to the periphery actually contributes to TPE. We examined the localization patterns of two nuclear with different levels of TPE: truncated VII-L and native VI-R. For both telomeres, localization to the nuclear Periphery or to the silencing foci was neither necessary nor sufficient for TPE. Moreover, there was no correlation between TPE levels and the extent. of localization. Tethering the truncated VII-L telomere to the nuclear periphery resulted in a modest increase in TPE. However, tethering did not bypass the roles of yKu70p, Sirp, or Esclp in TPE. Using Imitations in RIF genes that bypass the role of Ku in TPE, a correlation between the level of silencing and the number of Rap1p foci present in the nucleus was observed, Suggesting that Sir protein levels at telomeres determine both the level of TPE and the number of foci.