Nabeel-Shah S, Ashraf K, Saettone A, Garg J, Derynck J, Lambert JP, Pearlman RE, Fillingham J (2020) Nucleus-specific linker histones Hho1 and Mlh1 form distinct protein interactions during growth, starvation and development in Tetrahymena thermophila. Scientific reports 10(1):168 PUBMED:31932604
Akematsu T, Sánchez-Fernández R, Kosta F, Holzer E, Loidl J (2019) The Transmembrane Protein Semi1 Positions Gamete Nuclei for Reciprocal Fertilization in Tetrahymena. iScience 23(1):100749 PUBMED:31884169
Tian M, Loidl J (2019) An MCM family protein promotes interhomolog recombination by preventing precocious intersister repair of meiotic DSBs. PLoS genetics 15(12):e1008514 PUBMED:31815942
HHO1 knockouts show no global increase or decrease in the amount of transcription in the cell; however, these same knockouts also show that Hho1p is important for the transcriptional regulation of individual genes in response to stimuli, such as starvation. The differential regulation of Hho1p by phosphorylation under vegetative growth and starvation conditions has been well studied. During vegetative growth, Hho1p is phosphorylated on five closely spaced residues, preventing it from interacting with chromatin, likely by interfering with its ability to bind DNA. Under these conditions, expression is increased for CDC2, a homolog of the cyclin dependent kinases responsible for histone H1 phosphorylation, possibly creating a positive feedback loop that promotes the cell cycle. During starvation conditions, Hho1p is dephosphorylated, allowing it to bind to chromatin. This stimulates the expression of some genes, including ngoA, and protease genes such as CYP1, while inhibiting expression of other genes, such as CDC2. This decrease in CDC2 expression may be responsible for cell cycle arrest during starvation.
Associated Literature
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