Required for formation and/or maintenance of the proper nucleolar structure and function (By similarity). Plays a dual role in the regulation of ribosomal DNA (rDNA) transcription (By similarity). In the presence of high glucose, it maintains active rDNA transcription through H2A.Z deposition and under glucose starvation, is required for the repression of rDNA transcription, and this function may be independent of H2A.Z (By similarity). Interacts with CBX1, CBX3 and CBX5. Colocalizes with HP1 family proteins at pericentric heterochromatin. Belongs to the actin family. ARP6 subfamily.