Poster abstracts

Poster number 19 submitted by Pei Zhang

Identification of replication-dependent and replication-independent linker histone complexes

Pei Zhang (Department of Molecular and Cellular Biochemistry, Ohio State University), Owen Branson (Department of Molecular Virology, Immunology, and Medical Genetics), Michael Freitas (Department of Molecular Virology, Immunology, and Medical Genetics), Mark Parthun (Department of Molecular and Cellular Biochemistry, Ohio State University)

Abstract:
There are at least 11 different variants of linker histone H1 in mammalian cells, the sequences of which vary greatly in their C-terminal domains. The individual functions of H1 variants are not fully understood now. It was believed that H1 served as a global gene regulator by binding to chromatin unspecifically. However, previous researches found that while knocking out a single H1 variant might not lead to any observable phenotype, triple knockouts of H1 variants in mice has shown developmental defects and embryonic lethality. These observations suggest the hypothesis that each H1 variant has its individual function in the cells in addition to its roles as global chromatin modifiers. It is worth investigating whether the dynamics of replication dependent and independent variants of H1 are regulated by distinctive chaperones, similar to how core histones are regulated.

To answer this question, we are identifying the proteins associated with soluble forms of replication-dependent and replication-independent H1 variants. Tetracycline-inducible U2OS cell lines were generated to express 6xHis-tagged human histone H1.1 and H1.2 (replication-dependent variants), and H1.0 and H1.x (replication-independent variants). Soluble whole cell extracts made from those cell lines were purified by chromatography. Proteins associated with these H1 variants were identified by mass spectrometry. We found that some of the H1 variants form two separate complexes while others only exist in one complex. Importantly, we found that some linker histone associated factors associate with both replication-dependent and replication-independent H1 variants while other factors are specific for one type of histone H1. These findings will contribute to the understanding of the non-redundant functions of histone H1 variants, and to the possible new discoveries of proteins that impact chromatin structure by interacting with linker histones.

References:
[1]Yang, SM., et al., H1 linker histone promotes epigenetic silencing by regulating both DNA methylation and histone H3 methylation. PNAS, 2013 Jan 29;110(5):1708-13.

[2]Tagami, H., et al., Histone H3.1 and H3.3 complexes mediate nucleosome assembly pathways dependent or independent of DNA synthesis. Cell, 2004. 116(1): p. 51-61.

Keywords: Linker histones, Histone chaperones, DNA-binding protein complexes