Alternative mechanisms of transcriptional activation by Rap1p.
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.
Idrissi
F Z
FZ
Departament de Biologia Molecular i Cellular, Institut de Biologia Molecular de Barcelona, Consejo Superior de Investigaciones Cientificas, Jordi Girona, 18.08034 Barcelona, Spain.
Garcia-Reyero
N
N
Fernandez-Larrea
J B
JB
Piña
B
B
D015966:Gene Expression Regulation, Fungal; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015533:Transcriptional Activation; D020827:rap1 GTP-Binding Proteins / Q000235:genetics*
D020827:rap1 GTP-Binding Proteins