IDENTIFICATION OF COMPONENTS OF THE HIR COMPLEX REQUIRED FOR CHROMATIN ASSEMBLY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Nucleosomes are the fundamental building blocks of the eukaryotic chromosome, formed by wrapping DNA around histone proteins. The rapid and orderly deposition of histones on DNA is mediated by chromatin assembly proteins. In budding yeast, a set of four Hir proteins (Hir1, Hir2, Hir3, and Hpc2) identified genetically are known to act in concert with Asf1 to ensure proper deposition of histone tetramers (Sutton et al., Genetics, 2001; Sharp et al., Curr Biol, 2001). The Hir proteins also have a prominent role in maintaining the chromatin structure at the centromere, thereby contributing to accurate chromosome segregation (Sharp et al., Genes Dev, 2002). However, the biochemical nature of Hir protein complexes and their mechanisms for promoting proper chromatin assembly have remained largely unexplored. For example, almost nothing is known about the native oligomeric state of the Hir proteins, and previous genetic experiments do not indicate whether there may be undiscovered subunits of the complex. We therefore propose a structure/function approach by isolating native Hir protein complexes and characterizing them by both mass spectrometry and functional assays.