Heterochromatin

Heterochromatin is a tightly packed form of DNA, which comes in different varieties. These varieties lie on a continuum between the two extremes of constitutive and facultative heterochromatin. Both play a role in the expression of genes, where constitutive heterochromatin can affect the genes near them (position-effect variegation) and where facultative heterochromatin is the result of genes that are silenced through a mechanism such as histone methylation or siRNA through RNAi. Constitutive heterochromatin is usually repetitive and forms structural functions such as centromeres or telomeres, in addition to acting as an attractor for other gene-expression or repression signals. Facultative heterochromatin is not repetitive and although it shares the compact structure of constitutive heterochromatin, facultative heterochromatin can, under specific developmental or environmental signaling cues, lose its condensed structure and become transcriptionally active. Heterochromatin is often associated with the di and tri-methylation of H3K9.

Read more about HeterochromatinStructure, Function, Constitutive Heterochromatin, Facultative Heterochromatin, Yeast Heterochromatin

Other articles related to "heterochromatin":

CBX5 (gene)
... nuclear envelope • nucleoplasm • nuclear heterochromatin • nucleolus • cytoplasm • chromocenter • PML body • transcriptional repressor ... Heterochromatin protein-1 (HP1) is a methyl-lysine binding protein localized at heterochromatin sites, where it mediates gene silencing ...
Constitutive Heterochromatin
... Constitutive heterochromatin domains are sections of DNA that occur throughout the chromosomes of eukaryotes, but particularly at the centromeres and telomeres ... Unlike facultative heterochromatin, constitutive heterochromatin is never converted back into euchromatin ... The regions of DNA that exist as constitutive heterochromatin will be the same for all cells of a given species ...
Yeast Heterochromatin
... Saccharomyces cerevisiae, or budding yeast, is a model eukaryote and its heterochromatin has been defined thoroughly ... Fission yeast (Schizosaccharomyces pombe) uses another mechanism for heterochromatin formation at its centromeres ... in the initiation, propagation and maintenance of heterochromatin assembly ...
Spindle Checkpoint - Sister Chromatids Cohesion During Mitosis - The Role of Heterochromatin
... regions, and this suggested that the special structure or composition of heterochromatin might favour cohesin recruitment ... More recent studies indicate that the RNAi machinery regulates heterochromatin establishment, which in turn recruits cohesin to this region, both in S ... However, there must be other mechanisms than heterochromatin to ensure an augmented cohesion at centromeres, because S ...
RNA-induced Transcriptional Silencing
... methylation of lysine 9 of histone H3) which target the genomic region for heterochromatin formation ... pombe, and has been shown to be involved in the initiation and spreading of heterochromatin in the mating-type region and in centromere formation ... protein Chp1, and an argonaute interacting protein Tas3 which can also bind to Chp1, while heterochromatin formation has been shown to require at least argonaute and an RNA-dependent RNA polymerase ...