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2018 ; 8
(2
): 477-489
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Dependency of Heterochromatin Domains on Replication Factors
#MMPMID29187422
Jahn LJ
; Mason B
; Brøgger P
; Toteva T
; Nielsen DK
; Thon G
G3 (Bethesda)
2018[Feb]; 8
(2
): 477-489
PMID29187422
show ga
Chromatin structure regulates both genome expression and dynamics in eukaryotes,
where large heterochromatic regions are epigenetically silenced through the
methylation of histone H3K9, histone deacetylation, and the assembly of
repressive complexes. Previous genetic screens with the fission yeast
Schizosaccharomyces pombe have led to the identification of key enzymatic
activities and structural constituents of heterochromatin. We report here on
additional factors discovered by screening a library of deletion mutants for
silencing defects at the edge of a heterochromatic domain bound by its natural
boundary-the IR-R(+) element-or by ectopic boundaries. We found that several
components of the DNA replication progression complex (RPC), including
Mrc1/Claspin, Mcl1/Ctf4, Swi1/Timeless, Swi3/Tipin, and the FACT subunit Pob3,
are essential for robust heterochromatic silencing, as are the ubiquitin ligase
components Pof3 and Def1, which have been implicated in the removal of stalled
DNA and RNA polymerases from chromatin. Moreover, the search identified the
cohesin release factor Wpl1 and the forkhead protein Fkh2, both likely to
function through genome organization, the Ssz1 chaperone, the Fkbp39 proline
cis-trans isomerase, which acts on histone H3P30 and P38 in Saccharomyces
cerevisiae, and the chromatin remodeler Fft3. In addition to their effects in the
mating-type region, to varying extents, these factors take part in
heterochromatic silencing in pericentromeric regions and telomeres, revealing for
many a general effect in heterochromatin. This list of factors provides precious
new clues with which to study the spatiotemporal organization and dynamics of
heterochromatic regions in connection with DNA replication.
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