Patrick A. Grant
Associate Professor of Biochemistry & Molecular Genetics
Ph.D., Karolinska Institute, Sweden
Chromatin Modifications in Transcription

 

In the eukaryotic cell nucleus, DNA is packaged by histones into nucleosomes, the repeating subunits of chromatin. This packaging of DNA strongly inhibits transcription, hampering the binding of transcriptional activators to their cognate DNA sites and inhibiting transcription elongation.

A number of chromatin remodeling activities have been identified which assist transcriptional activators to overcome this barrier, by creating a localized alteration in chromatin strucutre. In addition to these activities the posttranslational acetylation of core histones has also been linked to the transcriptional capacity of chromatin for more than three decades. The acetylation of histones is catalyzed by histone acetyltransferases (HATs), which are often found to be associated with large multisubunit protein complexes that contain components with identity or homology to known regulators of transcription. In fact, a number of transcriptional coactivator proteins have now been identified as HATs, providing a direct molecular basis for the coupling of histone acetylation and transcriptional regulation. Why and how these proteins function as part of high molecular weight activities is not clearly understood however.

Our research has primarily focused on the identification and characterization of native HAT / transcriptional adaptor activities from the budding yeast Saccharomyces cerevisiae and to study their role in transcriptional activation. We have isolated multiple complexes, three of which are apparently dependent upon the coactivator Gcn5 for catalytic function in vitro and transcriptional activation of target genes in vivo. We found that Gcn5 is associated with Ada or Ada and Spt proteins in native complexes, fulfilling a number of genetic predictions which had indicated that these proteins function in a common pathway. however, it seems apparent that each HAT complex may have specific attributes conferred by certain uniquely associated proteins. We have largely concentrated our research on the SAGA (Spt-Ada-Gch5-Acetyltransferase) activity, which we recently resported also contains a third group of proteins, TAFIIs. Our research objectives deal with a structural and functional dissection of the components of SAGA and other related HAT complexes. This approach is designed to investigate the multifunctionality of these complexes in their specificity of acetylation, activator and basal factor interaction, promoter selectivity and transcriptional stimulation, in order to understand their relevance to and mechanism of gene activation.

An important aspect of a number of related HAT complexes has been the identification of an evolutionarily conserved component which has been directly linked to factors associated with certain cancers. This discovery provides a new avenue of investigation into how certain cancers may arise. Therefore, a clear understanding of how HAT complexes function is vital in order to understand their role in gene activation in health and disease.


Selected References

McCullough SD, Xu X, Dent SY, Bekiranov S, Roeder RG, Grant PA. (2012) "Reelin is a target of polyglutamine expanded ataxin-7 in human spinocerebellar ataxia type 7 (SCA7) astrocytes." Proc Natl Acad Sci U S A. Dec 109(52):21319-24. doi:10.1073/pnas.1218331110. Epub 2012 Dec 10. [PubMed]

Miller JL, Grant PA. (2012) "The role of DNA methylation and histone modifications in transcriptional regulation in humans." Subcell Biochem. 61:289-317. doi: 10.1007/978-94-007-4525-4_13. [PubMed]

Chen YC, Gatchel JR, Lewis RW, Mao CA, Grant PA, Zoghbi HY, Dent SY. (2012) "Gcn5 loss-of-function accelerates cerebellar and retinal degeneration in a SCA7 mouse model." Hum Mol Genet. Jan 21:394-405. doi: 10.1093/hmg/ddr474. Epub 2011 Oct 14. [PubMed]

Lee KK, Sardiu ME, Swanson SK, Gilmore JM, Torok M, Grant PA, Florens L, Workman JL, Washburn MP. (2011) "Combinatorial depletion analysis to assemble the network architecture of the SAGA and ADA chromatin remodeling complexes." Mol Syst Biol. Jul 7:503. doi: 10.1038/msb.2011.40. [PubMed]

Bian C, Xu C, Ruan J, Lee KK, Burke TL, Tempel W, Barsyte D, Li J, Wu M, Zhou BO,Fleharty BE, Paulson A, Allali-Hassani A, Zhou JQ, Mer G, Grant PA, Workman JL,Zang J, Min J. (2011) "Sgf29 binds histone H3K4me2/3 and is required for SAGA complex recruitment and histone H3 acetylation." EMBO J. Jun 30(14):2829-42. doi: 10.1038/emboj.2011.193. [PubMed]

Baker SP, Phillips J, Anderson S, Qiu Q, Shabanowitz J, Smith MM, Yates JR 3rd,Hunt DF, Grant PA. (2010) "Histone H3 Thr 45 phosphorylation is a replication-associated post-translational modification in S. cerevisiae." Nat Cell Biol. 12:294-8. doi: 10.1038/ncb2030. Epub 2010 Feb 7. [PubMed]

McCullough SD, Grant PA. (2010) "Histone acetylation, acetyltransferases, and ataxia--alteration of histone acetylation and chromatin dynamics is implicated in the pathogenesis of polyglutamine-expansion disorders." Adv Protein Chem Struct Biol. 79:165-203. doi:10.1016/S1876-1623(10)79005-2. [PubMed]

Baker SP, Grant PA. (2007) "The SAGA continues: expanding the cellular role of a transcriptional co-activator complex." Oncogene. Aug 26(37):5329-40. [PubMed]

McMahon SJ, Pray-Grant MG, Schieltz D, Yates JR 3rd, Grant PA. (2005) "Polyglutamine-expanded spinocerebellar ataxia-7 protein disrupts normal SAGA and SLIK histone acetyltransferase activity." Proc Natl Acad Sci U S A. Jun 102(24):8478-82. Epub 2005 Jun 2. [PubMed]

Pray-Grant MG, Daniel JA, Schieltz D, Yates JR 3rd, Grant PA. (2005) "Chd1 chromodomain links histone H3 methylation with SAGA- and SLIK-dependent acetylation." Nature. Jan 433(7024):434-8. Epub 2005 Jan 12. [PubMed]