Component of the Clr4 methyltransferase complex (ClrC) which contributes to the establishment of heterochromatin by specifically methylating histone H3 to form H3K9me (PubMed:16024659, PubMed:8138176, PubMed:15372076). ClrC preferentially ubiquitylates H3K14 and ClrC-mediated H3 ubiquitination promotes clr4 methyltransferase activity for the methylation of H3K9 (PubMed:31468675). H3K9me represents a specific tag for epigenetic transcriptional repression by recruiting swi6/HP1 to methylated histones which leads to transcriptional silencing within centromeric heterochromatin, telomeric regions and at the silent mating-type loci (PubMed:16024659, PubMed:8138176, PubMed:7851795, PubMed:10766735). Rik1 is involved in the RNAi-mediated targeting of ClrC to heterochromatic repeat elements (PubMed:17114925, PubMed:18345014). Rik1 has also a function in meiotic telomere clustering (PubMed:15197176). Component of the Clr4 methyltransferase complex (ClrC) composed of at least clr4, rik1, pcu4, rbx1, raf1 and raf2. The cullin pcu4, rik1, raf1, raf2 and the ring-box protein rbx1 are components of an E3 ubiquitin ligase, whose activity is essential for heterochromatin assembly. Cells show derepressed silent mating-type cassettes. Belongs to the DDB1 family.