Gene silencing in S. pombe occurs by heterochromatin formation at the centromere (cen), mating-type (mat)and telomere loci. It is mediated by silencing factors including Swi6, Clr1-4, Rhp6 and Pol-alpha. RNAi pathwayalso plays a role in establishment of silencing at the mat and cen loci. Recently, the stress response factors, Atf1and Pcr1were shown to play an RNAi-independent role in silencing at the mat3 locus through a cis-actingAtf1-binding site located within the repression element REIII and recruitment of the silencing factors Clr3 andClr6. Another cis-acting site, named repression element REII abutting the mat2 locus, also establishes heterochromatinstructure through Clr5 and histone deacetylases but independently of H3-Lys9-methylation andRNAi. Here, we report the occurrence of binding sites for another oxidative response factor, the pombe AP1-like factor Pap1, at the mating-type, centromere and telomere loci. By genetic studies we show that these sitesplay a role in silencing at the outer repeats of centromeres as well as mating-type locus and this effect ismediated through Pap1 binding site and interaction with and recruitment of the HP1/Swi6. Importantly, pap1-Deltacells display a silencing defect even in absence of the oxidative stress. Such a role of Pap1 in heterochromatinformation may be evolutionarily conserved.
Volume 48, 2023
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