Question: What is the function of yeast Clr4 on chromatin?

Context:
Mutations in the clr4+, rik1+ and swi6+ genes dramatically reduce silencing at certain centromeric regions and cause elevated chromosome loss rates
The Swi6 protein was found to be delocalised from all three silent chromosomal regions, and dispersed within the nucleus, in both clr4 and rik1 mutant cells. 
Mutations in clr4, rik1 and swi6 also result in elevated sensitivity to reagents which destabilise microtubules and show a synergistic interaction with a mutation in the beta-tubulin gene (nda3).
These observations suggest that clr4+ and rik1+ must play a role in the assembly of Swi6p into a transcriptionally silent, inaccessible chromatin structure at fission yeast centromeres which is required to facilitate interactions with spindle microtubules and to ensure normal chromosome segregation.
The chromo and SET domains of the Clr4 protein are essential for silencing in fission yeast.
Like Su(var)3-9p, Clr4p contains SET and chromo domains, motifs found in proteins that modulate chromatin structure.
Surprisingly, RNA differential display experiments demonstrated that clr4+ can mediate transcriptional activation of certain other loci.
These results show that clr4 plays a critical role in silencing at mating-type loci and centromeres through the organization of repressive chromatin structure and demonstrate a new, activator function for Clr4p.
Clr4 is known to regulate silencing and switching at the mating-type loci and to affect chromatin structure at centromeres. 
Mutations in Cul4 result in defective localization of Clr4 and loss of silencing at heterochromatic loci.
The Clr4 methyltransferase determines the subnuclear localization of the mating-type region in fission yeast.
In a strain lacking the histone methyltransferase Clr4, crucial for the formation of heterochromatin, the mating-type region had a random localization in the nucleus.
Cut4 and Cut9 interact directly with Swi6/HP1 and Clr4, whereas the mutant Cut4 does not, suggesting that a direct physical interaction of APC subunits Cut4 and Cut9 with Swi6 and Clr4 is instrumental in heterochromatin assembly.
Thus, APC and heterochromatin proteins Swi6 and Clr4 play a mutually cooperative role in heterochromatin assembly, thereby ensuring chromosomal integrity, inheritance, and segregation during mitosis and meiosis.
Positive feedback mechanisms that link the RNAi pathway and the Clr4/Suv39h1 histone H3K9 methyltransferase complex (Clr-C) result in requirements for H3K9 methylation for full siRNA production and for siRNA production to achieve full histone methylation.
Heterochromatin assembly in fission yeast depends on the Clr4 histone methyltransferase, which targets H3K9.
These analyses place Sir2 and H3K14 deacetylation upstream of Clr4 recruitment during heterochromatin assembly.
These results show that clr4 plays a critical role in silencing at mating-type loci and centromeres through the organization of repressive chromatin structure and demonstrate a new, activator function for Clr4p
These results show that clr4 plays a critical role in silencing at mating-type loci and centromeres through the organization of repressive chromatin structure and demonstrate a new, activator function for Clr4p..

Answer: Clr4 is known to regulate silencing and switching at the mating-type loci and to affect chromatin structure at centromeres. The Clr4 methyltransferase determines the subnuclear localization of the mating-type region in fission yeast. Heterochromatin assembly in fission yeast depends on the Clr4 histone methyltransferase, which targets H3K9.