Monday, September 24, 2007
Friday, August 10, 2007
Thursday, August 2, 2007
Tuesday, July 31, 2007
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.)
Monday, July 23, 2007
Saturday, July 21, 2007
Exploring the Dark Matter of the Genome
June 18, 2007 - Not so long ago, the difficult-to-sequence, highly repetitive, gene-poor DNA found in regions of chromosomes known as heterochromatin was called "junk." Like dark matter in the universe, the true nature of heterochromatin was unknown.
Now members of the Drosophila Heterochromatin Genome Project (DHGP), headed by Gary Karpen of the Department of Energy's Lawrence Berkeley National Laboratory, are approaching a complete assembly, mapping, and functional analysis of those portions (other than simple repeats) of the heterochromatic DNA of Drosophila melanogaster, the fruit fly. The results confirm that heterochromatin is far from mere junk.
"Most researchers thought heterochromatin had little or no function, because it appeared to lack the protein-coding genes that occur so richly in the chromosomes' more accessible and better-studied euchromatin," says Karpen, a senior scientist in Berkeley Lab's Life Sciences Division and an adjunct professor of cell and molecular biology at the University of California at Berkeley. "In recent years it has become apparent that heterochromatin is critical for many essential functions...... http://www.brightsurf.com/news/headlines/31165/Exploring_the_Dark_Matter_of_the_Genome.html