The coordinated replication and transcription of pericentromeric repeats enable 
RNA interference (RNAi)-mediated transmission of pericentromeric heterochromatin 
in fission yeast, which is essential for the proper function of centromeres. 
Rad3/ATR kinase phosphorylates histone H2A on serine-128/-129 to create γH2A in 
pericentromeric heterochromatin during S phase, which recruits Brc1 through its 
breast cancer gene 1 protein (BRCA1) C-terminal (BRCT) domains. Brc1 prevents 
the collapse of stalled replication forks; however, it is unknown whether this 
activity influences centromere function. Here, we show that Brc1 localizes in 
pericentromeric heterochromatin during S phase, where it enhances 
Clr4/Suv39-mediated H3 lysine-9 dimethylation (H3K9me2) and gene silencing. Loss 
of Brc1 increases sensitivity to the microtubule-destabilizing drug 
thiabendazole (TBZ) and increases chromosome missegregation in the presence of 
TBZ. Brc1 retains significant function even when it cannot bind γH2A. However, 
elimination of the serine-121 site on histone H2A, a target of Bub1 spindle 
assembly checkpoint kinase, sensitizes γH2A-deficient and brc1Δ cells to 
replication stress and microtubule destabilization. Collective results suggest 
that Brc1-mediated stabilization of stalled replication forks is necessary for 
fully efficient transmission of pericentromeric heterochromatin, which is 
required for accurate chromosome segregation during mitosis.