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Heterochromatin is usually localized to the periphery of the nucleus. Despite this early dichotomy, recent evidence in both animals [9] and plants [10] has suggested that there are more than two distinct heterochromatin states, and it may in fact exist in four or five 'states', each marked by different combinations of epigenetic marks.
Distinction between Euchromatin and Heterochromatin. Euchromatin (also called "open chromatin") is a lightly packed form of chromatin (DNA, RNA, and protein) that is enriched in genes, and is often (but not always) under active transcription. Euchromatin stands in contrast to heterochromatin, which is tightly packed and less accessible for ...
Possible models for expression of genes found in constitutive heterochromatin. [5] Heterochromatin vs. euchromatin. Constitutive heterochromatin is found more commonly in the periphery of the nucleus attached to the nuclear membrane. This concentrates the euchromatic DNA in the center of the nucleus where it can be actively transcribed.
In other words, the heterochromatin spreads and causes gene silencing by packaging the normally euchromatic region. [2] But this model fails to explain some aspects of PEV. For example, variegation can be induced in a gene located several megabases from the heterochromatin-euchromatin breakpoint due to rearrangements in that breakpoint.
Once added to the histone, these groups (directly or indirectly) elicit either a loose and open histone conformation, euchromatin, or a tight and closed histone conformation, heterochromatin. Euchromatin marks active transcription and gene expression, as the light packing of histones in this way allows entry for proteins involved in the ...
This relaxation can be reversed by deacetylation catalyzed by HDAC activity. Relaxed, transcriptionally active DNA is referred to as euchromatin. More condensed (tightly packed) DNA is referred to as heterochromatin. Condensation can be brought about by processes including deacetylation and methylation. [1]
The level of nucleosomal packaging can have profound consequences on all DNA-mediated processes including gene regulation. Euchromatin (loose or open chromatin) structure is permissible for transcription whereas heterochromatin (tight or closed chromatin) is more compact and refractory to factors that need to gain access to the DNA template.
Heterochromatin vs. euchromatin. An active chromatin sequence (ACS) is a region of DNA in a eukaryotic chromosome in which histone modifications such as acetylation lead to exposure of the DNA sequence thus allowing binding of transcription factors and transcription to take place. Active chromatin may also be called euchromatin.