Heterochromatic RNA are targeted by RNAi which recruits the H3K9 methyltransferase to establish heterochromatin, but their uncontrolled accumulation hinders heterochromatin formation. This thesis shows that elimination of heterochromatic transcripts on the chromatin by RNAi and the Ccr4-Not complex is required for heterochromatin assembly. We propose that accumulation of chromatin-bound lncRNA interferes with heterochromatin organization and promotes chromatin opening.