Tian M, Loidl J (2018) A chromatin-associated protein required for inducing and limiting meiotic DNA double-strand break formation. Nucleic acids research ( ): PUBMED:30357385
Ali EI, Loidl J, Howard-Till RA (2018) A streamlined cohesin apparatus is sufficient for mitosis and meiosis in the protist Tetrahymena. Chromosoma ( ): PUBMED:29948142
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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Ref:12351190: Udani RA, Karrer KM (2002) ASI1, a gene encoding a novel leucine zipper protein, is induced during development of the macronucleus in Tetrahymena. Mechanisms of development 118(1-2):215-8
Ref:10983971: Dou Y, Gorovsky MA (2000) Phosphorylation of linker histone H1 regulates gene expression in vivo by creating a charge patch. Molecular cell 6(2):225-31
Ref:10207086: Huang H, Smothers JF, Wiley EA, Allis CD (1999) A nonessential HP1-like protein affects starvation-induced assembly of condensed chromatin and gene expression in macronuclei of Tetrahymena thermophila. Molecular and cellular biology 19(5):3624-34
Ref:9163512: Suzuki KM, Hosoya N, Takahashi T, Kosaka T, Hosoya H (1997) Release of a newly-identified cysteine protease, tetrain, from Tetrahymena into culture medium during the cell growth. Journal of biochemistry 121(4):642-7
Ref:8756729: Shen X, Gorovsky MA (1996) Linker histone H1 regulates specific gene expression but not global transcription in vivo. Cell 86(3):475-83
Ref:8464925: Karrer KM, Peiffer SL, DiTomas ME (1993) Two distinct gene subfamilies within the family of cysteine protease genes. Proceedings of the National Academy of Sciences of the United States of America 90(7):3063-7
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