Why is heterochromatin transcriptionally inactive?

Why is heterochromatin transcriptionally inactive?

Heterochromatin is densely packed and inaccessible to transcription factors so it is rendered transcriptionally silent (Richards and Elgin 2002). Euchromatin, on the other hand, is less condensed, more accessible, and therefore transcriptionally active (Hennig 1999).

What stops heterochromatin from spreading?

(C) Nucleosome free regions prevent the spreading of heterochromatin modifications to establish heterochromatin boundaries.

What does heterochromatin protein do?

Initially discovered to be a major constituent of heterochromatin important for gene silencing, HP1 is now known to be a dynamic protein that also functions in transcriptional elongation, centromeric sister chromatid cohesion, telomere maintenance and DNA repair.

What type of chromatin is transcriptionally active?

Euchromatin is the transcriptionally active form of chromatin. On the other hand, heterochromatin exists in condensed form and is usually present toward the end or pericentric region of the chromosome.

What causes heterochromatin spreading?

The spreading and inheritance of heterochromatin are believed to be dependent on preexisting H3K9 tri-methylation (H3K9me3), which is recognized by the histone methyltransferase Clr4/Suv39h via its chromodomain, to promote further deposition of H3K9me.

How does HP1 promote heterochromatin formation?

Recent studies show that HP1 proteins play an important role in heterochromatin by interacting with histones H3 and H4 and methyltransferase enzymes. The binding of the HP1 CD to poly-methylated H3 lysine 9 (H3K9me2/3) and H1. 4K26me85 triggers a silencing mechanism, resulting in the formation of heterochromatin.

What is heterochromatin euchromatin?

Heterochromatin is defined as the area of the chromosome which is darkly stained with a DNA specific stain and is in comparatively condensed form. Euchromatin is defined as the area of the chromosome which is rich in gene concentration and actively participates in the transcription process.

Why is euchromatin transcriptionally active chromatin?

Transcription. Euchromatin participates in the active transcription of DNA to mRNA products. The unfolded structure allows gene regulatory proteins and RNA polymerase complexes to bind to the DNA sequence, which can then initiate the transcription process.