ABSTRACT
Methylation of histone proteins is one of their many modifications that affect chromatin structure and regulate gene expression. Methylation of histone H3 on lysines 4 and 79, catalyzed by the Set1-containing complex COMPASS and Dot1p, respectively, is required for silencing of expression of genes located near chromosome telomeres in yeast. We report that the Paf1 protein complex, which is associated with the elongating RNA polymerase II, is required for methylation of lysines 4 and 79 of histone H3 and for silencing of expression of a telomere-associated gene. We show that the Paf1 complex is required for recruitment of the COMPASS methyltransferase to RNA polymerase II and that the subunits of these complexes interact physically and genetically. Collectively, our results suggest that the Paf1 complex is required for histone H3 methylation, therefore linking transcriptional elongation to chromatin methylation.
Subject(s)
DNA-Binding Proteins/metabolism , Genome, Fungal , Histone-Lysine N-Methyltransferase , Histones/metabolism , Methyltransferases/metabolism , Nuclear Proteins/metabolism , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/genetics , Transcription Factors/metabolism , Transcription, Genetic , Blotting, Western , Chromatin/metabolism , DNA Methylation , Electrophoresis, Polyacrylamide Gel , Gene Silencing , Histone Methyltransferases , Lysine/chemistry , Methylation , Methyltransferases/chemistry , Models, Genetic , Mutation , Precipitin Tests , Protein Binding , Protein Methyltransferases , Proteome , RNA Polymerase II/metabolism , Saccharomyces cerevisiae/metabolism , Telomere/metabolismABSTRACT
Ubiquitination of histone H2B catalyzed by Rad6 is required for methylation of histone H3 by COMPASS. We identified Bre1 as the probable E3 for Rad6's role in transcription. Bre1 contains a C3HC4 (RING) finger and is present with Rad6 in a complex. The RING finger of Bre1 is required for ubiquitination of histone H2B, methylation of lysine 4 and 79 of H3 and for telomeric silencing. Chromatin immunoprecipitation experiments indicated that both Rad6 and Bre1 are recruited to a promoter. Bre1 is essential for this recruitment of Rad6 and is dedicated to the transcriptional pathway of Rad6. These results suggest that Bre1 is the likely E3 enzyme that directs Rad6 to modify chromatin and ultimately to affect gene expression.
