Ccq1-Tpz1^TPP1interaction facilitates telomerase and SHREC association with telomeres in fission yeast

Abstract

Through characterization of ccq1 mutants that disrupt Ccq1-Tpz1TPP1 interaction, the authors establish that Ccq1-Tpz1TPP1 interaction contributes to optimal binding of the Ccq1-SHREC complex and is required for Ccq1 Thr93 phosphorylation and telomerase recruitment.

Fission yeast Ccq1 is a modulator of telomerase activity

“…Interestingly, truncations of the C-terminus to eliminate the coiled-coil motifs (lanes [1–441] and [1–500]) led to slight elongation of telomeres, implying that the C-terminus of Ccq1 is involved in negatively regulating telomere extension. This was unexpected as Ccq1 was thought to act solely as a positive regulator of telomerase and contradicted current knowledge ( 41 ). The series of Ccq1 truncations were relatively well expressed compared to full length Ccq1, except for the 1–424 and 1–400 fragments, which had significantly reduced expression ( Supplementary Figure S2B ).…”

“…Elimination of endogenous Ccq1 in strains expressing the Ccq1-Est1 chimera led to efficient telomerase recruitment and elongation of telomeres, indicating that endogenous Ccq1 is able to suppress the function of the Ccq1-Est1 chimera. Although Ccq1 is an abundant protein compared to Tpz1 ( 41 ), the negative regulation by endogenous Ccq1 was not simply caused by competitive occupation of Tpz1 against the Ccq1-Est1 chimera. Truncation analysis of endogenous Ccq1 showed that this elongation effect was also seen in strains with a C-terminal truncation of endogenous Ccq1 (amino acids 1–441) (Figure 3A : lane ccq1(1–441) in ccq1-est1 ), suggesting that a negative regulatory effect requires the Ccq1 C-terminus.…”

“…Deletion of clr3 and clr4 leads to disruption of both telomeric and centromeric gene silencing, and deletion of taz1 leads to disruption of only telomeric gene silencing (Figure 6B ). A recent study showed that C-terminal truncation of Ccq1 recaptures the telomeric gene-silencing defect shown in ccq1 Δ cells ( 41 ). We confirmed that our ccq1(1–441) truncation activated the telomere-adjacent gene ura4 + , resulting in cellular sensitivity to 5-FOA.…”

Shelterin and subtelomeric DNA sequences control nucleosome maintenance and genome stability

“…In agreement with the findings for ccq1Δ, the loss of H3 in mutants of CLRC is specific for TAS and not seen at tlh1 + ( Fig 3B). Ccq1 was further shown to interact with the HDAC Clr3, which is part of the repressor complex SHREC that also contains the Snf2-like nucleosome remodeler Mit1 ( Fig 3A) [9,21,22,29]. Mit1 and Clr3 have been associated with nucleosome positioning and turnover and prevent the formation of nucleosome-depleted regions within heterochromatin [21,[29][30][31].…”

“…In humans and Schizosaccharomyces pombe, telomere protection is mediated by the shelterin complex, which consists of six subunits ( Fig 1A): Pot1 (hPOT1); Tpz1 (hTPP1); Poz1 (hTIN2); Rap1; Taz1 (hTRF1 and hTRF2) [1][2][3][4]. Fission yeast has an additional subunit Ccq1, which associates with shelterin via Tpz1 and is essential for maintaining telomere length through recruiting telomerase [2,[5][6][7][8][9][10]. When telomeres shorten to a critical size (after about 100 generations), cells undergo telomere crisis resulting in cell cycle arrest and cellular senescence [11].…”