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Sci Rep. 2020 Jan 13;10(1):168. doi: 10.1038/s41598-019-56867-0.

Nucleus-specific linker histones Hho1 and Mlh1 form distinct protein interactions during growth, starvation and development in Tetrahymena thermophila.

Author information

1
Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada.
2
Donnelly Centre, University of Toronto, Toronto, M5S 3E1, Canada.
3
Department of Molecular Genetics, University of Toronto, Toronto, M5S 1A8, Canada.
4
Department of Biology, York University, 4700 Keele St., Toronto, M3J 1P3, Canada.
5
Department of Molecular Medicine and Cancer Research Centre, Université Laval, Quebec, Canada.
6
CHU de Québec Research Center, CHUL, 2705 Laurier Boulevard, Quebec, G1V 4G2, Canada.
7
Department of Biology, York University, 4700 Keele St., Toronto, M3J 1P3, Canada. ronp@yorku.ca.
8
Department of Chemistry and Biology, Ryerson University, 350 Victoria St., Toronto, M5B 2K3, Canada. jeffrey.fillingham@ryerson.ca.

Abstract

Chromatin organization influences most aspects of gene expression regulation. The linker histone H1, along with the core histones, is a key component of eukaryotic chromatin. Despite its critical roles in chromatin structure and function and gene regulation, studies regarding the H1 protein-protein interaction networks, particularly outside of Opisthokonts, are limited. The nuclear dimorphic ciliate protozoan Tetrahymena thermophila encodes two distinct nucleus-specific linker histones, macronuclear Hho1 and micronuclear Mlh1. We used a comparative proteomics approach to identify the Hho1 and Mlh1 protein-protein interaction networks in Tetrahymena during growth, starvation, and sexual development. Affinity purification followed by mass spectrometry analysis of the Hho1 and Mlh1 proteins revealed a non-overlapping set of co-purifying proteins suggesting that Tetrahymena nucleus-specific linker histones are subject to distinct regulatory pathways. Furthermore, we found that linker histones interact with distinct proteins under the different stages of the Tetrahymena life cycle. Hho1 and Mlh1 co-purified with several Tetrahymena-specific as well as conserved interacting partners involved in chromatin structure and function and other important cellular pathways. Our results suggest that nucleus-specific linker histones might be subject to nucleus-specific regulatory pathways and are dynamically regulated under different stages of the Tetrahymena life cycle.

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