Abstract
A study of gene silencing within the mating-type region of fission yeast defines two distinct pathways responsible for the establishment of heterochromatin assembly. One is RNA interference-dependent and acts on centromere-homologous repeats (cenH). The other is a stochastic Swi6 (the fission yeast HP1 homolog)-dependent mechanism that is not fully understood. Here we find that activating transcription factor (Atf1) and Pcr1, the fission yeast bZIP transcription factors homologous to human ATF-2, are crucial for proper histone deacetylation of both H3 and H4. This deacetylation is a prerequisite for subsequent H3 lysine 9 methylation and Swi6-dependent heterochromatin assembly across the rest of the silent mating-type (mat) region lacking the RNA interference-dependent cenH repeat. Moreover, Atf1 and Pcr1 can form complexes with both a histone deacetylase, Clr6, and Swi6, and clr6 mutations affected the H3/H4 acetylation patterns, similar to the atf1 and pcr1 deletion mutant phenotypes at the endogenous mat loci and at the ctt1+ promoter region surrounding ATF/CRE-binding site. These data suggest that Atf1 and Pcr1 participate in an early step essential for heterochromatin assembly at the mat locus and silencing of transcriptional targets of Atf1. Furthermore, a phosphorylation event catalyzed by the conserved mitogen-activated protein kinase pathway is important for regulation of heterochromatin silencing by Atf1 and Pcr1. These findings suggest a role for the mitogen-activated protein kinase pathway and histone deacetylase in Swi6-based heterochromatin assembly.
Highlights
Methylation of histone H3 lysine 9 (H3 Lys-9) by the conserved H3 Lys-9-specific methyltransferase, Su(var)3-9 in flies, SUV39H1 in human, and Clr4 in the fission yeast Schizosaccharomyces pombe [1,2,3,4] correlates with heterochromatin assembly
We find that cooperation of the ATF/CREB transcription factors with common silencing factors including histone deacetylase Clr6 and Swi6 protein is important for histone deacetylation and H3 Lys-9 methylation via an additional RNA interference (RNAi)-independent, Swi6-dependent mechanism that acts across the rest of the silent mat locus in the absence of centromere-homologous repeats (cenH) repeats
To identify factors important for the stochastic heterochromatin assembly in an RNAi-independent, Swi6-dependent manner, we investigated the roles of bZIP transcription factors in heterochromatin silencing at the mating-type region
Summary
Genotype hϩ otr1R (SphI)::ade6ϩ ura4-D18 ade6-DN/N leu h90 mat3(EcoRV)::ade6ϩ ura4-D18 ade6-DN/N hϩ leu ade6-DN/N Ch16-LEU2-ade6ϩ-tel mat1-Msmt-0 L(Sac1)::ade6ϩ ade6-M210 leu ura4-D18 mat1-Msmt-0 L(BglII)::ade6ϩ ade6-M210 leu ura4-D18. Ing [21], there is still no clear evidence addressing the function of Atf and Pcr in heterochromatin silencing. We describe how the ATF/CREB transcription factors regulate a Swi6-dependent heterochromatin assembly in fission yeast. We find that cooperation of the ATF/CREB transcription factors with common silencing factors including histone deacetylase Clr and Swi protein is important for histone deacetylation and H3 Lys-9 methylation via an additional RNAi-independent, Swi6-dependent mechanism that acts across the rest of the silent mat locus in the absence of cenH repeats
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