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The role of ING homologs in the yeast Saccharomyces cerevisiae Martin, David Greg Edward

Abstract

The yeast inhibitor of growth (ING) homolog, Ynglp, was identified based on sequence similarity of its highly conserved plant homeodomain (PHD) finger with other ING family members. Ynglp has been shown to be a stable subunit of the NuA3 histone acetyltransferase (HAT) complex. While previous work has indicated the requirement of Ynglp for NuA3 function, little was known regarding its role within the NuA3 complex. The &4.SJ-dependent HAT NuA3 was characterized through in vitro studies as having specificity towards histone H3. Whether NuA3 acetylates histones in vivo or what factors influence the binding of NuA3 with the nucleosome was also unknown. Using a chromatin pull-down assay, in conjunction with genetic studies, we show that Ynglp is required by NuA3 for its interaction with the nucleosome, and this interaction occurs within the histone H3 tail. Additionally, we show that mutation of lysine 14, the preferred site of NuA3 acetylation in vitro, shows the same phenotype as a sas3A specific phenotype indicating that modification of this residue is important for NuA3 function. The interaction of NuA3 is dependent upon Setlp and Set2p methyltransferases, as well as their substrates, histone H3 lysine residues 4 and 36 respectively. These results indicate that NuA3 is functioning as a histone acetyltransferase in vivo, and that methylation serves as a mark for the recruitment of NuA3 to the nucleosome. Through the use of additional chromatin pull-down experiments, we extend our investigation to assess whether two other yeast TNG homologs, Yng2p and Pho23p, (found in the NuA4 HAT and Rpd3-Sin3 histone deacetylase complexes respectively) perform similar functions to Ynglp within their respective complexes. Finally, we show that over-expression of human ING2, like YNG1, is toxic within yeast. Having shown that Ynglp interacts with the nucleosome, we discuss the possibility of human ING proteins functioning in a similar manner.

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