RNA-guided Epigenetic Control of Gene Expression

As little as 10% of the genome is coding DNA. The rest of the genome is non-coding and is comprised of a diverse family of repeating sequences (e.g. cen, mat, IES). These DNA repeats are foci for the generation and accumulation of short heterochromatic RNA (shRNAs). shRNAs are important for the regulation of heterochromatin initiation and formation. Double stranded shRNAs undergo RNAi-like processing involving dicer (dcr), RdRp (RNA dependent RNA polymerase), argonaute (ago) and Twi1 (piwi-related gene of the argonaute family). The processed shRNA is thought to interact with Chromo domain containing proteins (e.g. Chp1, Pdd1). The resultant complex is the molecular link between DNA target sequence (through pairing with the shRNA), HP1 (Heterchromatin Protein 1), histone H3 methylation and DNA methylation. (Black: genomic region. Purple: DNA repeats. Green: a gene or transcription unit (green). Blue: Promoter-driven mRNA. Dashed blue: intergenic transcription.)

Back to Top

Adapted from Jenuwein, T. Science, 297, 2215, (2002).