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Connecting the histone acetyltransferase complex SAS-I to the centromere in S. cerevisiae


Seitz,  Stefanie
Max Planck Society;

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Seitz, S. (2004). Connecting the histone acetyltransferase complex SAS-I to the centromere in S. cerevisiae. PhD Thesis, Humboldt-Universität, Berlin.

The essential histone H3 variant Cse4 plays a crucial role at the centromere in S.cerevisiae, where it replaces histone H3 in that it assembles centromere specific (Cse4-H4)2 tetrameres. We found in our study that the histone H3 variant was able to interact over its unique N-Terminus with two subunits of the histone acetyltransferase complex SAS-I: Sas2 and Sas4. Mutations within the acetyl-CoA binding site (HAT domain) or the zink-finger of Sas2 disrupted the binding to Cse4, although an indirect interaction was found with o-immunoprecipitation experiments. Additionally, the N-terminus of Cse4 interacted with Cac1, the largest subunit of the chromatin assembly factor CAF-I and Asf1 – two histone chaperones that assemble histones H3 and H4 into nucleosomes. Our findings further suggest a role of Cac1 independent of Cac2 and Cac3 as no binding to Cse4 could be detected. A role for Sas2 at the centromere was further confirmed in that a sas2 deletion (sas2 delta) disrupted the binding of Cse4 to Ctf19. Additionally, sas2 delta partially rescued the temperature sensitivity of a cse4-103 mutated strain at elevated temperatures, suggesting a role for Sas2 in improving centromere stability. An important question resulted from our studies: is Sas2 able to acetylate the histone H3 variant Cse4 ? We have circumstantial evidence that Cse4 was indeed acetylated in the cell, but whether Sas2 accounts for the acetylation remains to be determined.