Abstract
To explore the role of RNAi –dependent mechanisms in maintaining heterochromatic structures in vertebrates, we have determined the distribution of binding sites for the protein Argonaute2 (hAgo2) in repeat sequences of the human cell line K562. Ago2 is associated with silent regions of the genome, and preferentially bound to silent satellite repeats. Peaks of hAgo2 binding in satellites were associated with roughly equal amounts of both sense and anti‐sense transcripts, were enriched for both histone H3 lysine 9 tri‐ and dimethylation, and depleted for acetylation of H3 lysine 9 and H4 lysine 16. Surprisingly, hAgo2 peaks and satellite repeats were enriched for nucleolar small RNAs and genomic regions known to associate with the nucleolus. Immunofluorescence indicated that hAgo2 and the remnants of the nucleolus co‐localized during mitosis in the vicinity of the chromosomes and the mitotic spindle. This work supports our previously published model of RNAi‐mediated maintenance of heterochromatin structure.
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