Protosilencers in Saccharomyces cerevisiae Subtelomeric Regions

Corresponding author: Eric Gilson, Laboratoire de Biologie Moléculaire et Cellulaire, UMR5665 CNRS/ENSL, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69364 Lyon Cedex 07, France., Eric.Gilson{at}ens-lyon.fr (E-mail)

Communicating editor: S. HENIKOFF

Saccharomyces cerevisiae subtelomeric repeats contain silencing elements such as the core X sequence, which is present at all chromosome ends. When transplaced at HML, core X can enhance the action of a distant silencer without acting as a silencer on its own, thus fulfilling the functional definition of a protosilencer. Here we show that an ACS motif and an Abf1p-binding site participate in the silencing capacity of core X and that their effects are additive. In addition, in a variety of settings, core X was found to bring about substantial gene repression only when a low level of silencing was already detectable in its absence. Adjoining an X-STAR sequence, which naturally abuts core X in subtelomeric regions, did not improve the silencing capacity of core X. We propose that protosilencers play a major role in a variety of silencing phenomena, as is the case for core X, which acts as a silencing relay, prolonging silencing propagation away from telomeres.

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