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J. Biol. Chem., Vol. 276, Issue 28, 26090-26098, July 13, 2001

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Alternative Mechanisms of Transcriptional Activation by Rap1p^*

Fatima-Zahra Idrissi, Natalia Garcia-Reyero, Juan B. Fernandez-Larrea, and Benjamin Piña^§

From the Departament de Biologia Molecular i Cellular, Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Científicas, Jordi Girona, 18.08034 Barcelona, Spain

Single Rap1p DNA-binding sites are poor activators of transcription of yeast minimal promoters, even when fully occupied in vivo. This low efficiency is due to two independent repression mechanisms as follows: one that requires the presence of histones, and one that requires Hrs1p, a component of the RNA polymerase II mediator complex. Both repression mechanisms were greatly reduced for constructs with tandemly arranged sites. In these constructs, UASrpg sequences (ACACCCATACATTT) activated better than telomere-like sequences (ACACCCACACACCC) in an orientation-dependent manner. Both mutations in the SWI/SNF complex and a deletion of amino acids 597-629 of Rap1p (Tox domain) decreased synergistic effects of contiguous telomeric sites. Conversely, deletion of amino acids 700-798 of Rap1p (Sil domain) made UASrpg and telomeric sites functionally indistinguishable. We propose that the Sil domain masks the main transactivation domain of Rap1p in Rap1p-telomere complexes, where the Tox domain behaves as a secondary activation domain, probably by interacting with chromatin-remodeling complexes. Rap1p DNA-binding sites in ribosomal protein gene promoters are mainly UASrpg-like; their replacement by telomeric sequences in one of these promoters (RPS17B) decreased transcription by two-thirds. The functional differences between UASrpgs and telomeric sequences may thus contribute to the differential expression of Rap1p-regulated promoters in vivo.

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