Heterochromatin Formation and Gene Silencing

Question 1

Is Constitutive Heterochromatin (cHC) able to decondense?

Answer 1

No

Question 2

Which DNA sequences are found in cHC?

Answer 2

Telomeres, centromeres, repetitive seqs, satellite DNA

Question 3

Is cHC stably inherited?

Answer 3

Yes

Question 4

Is facilitative HC (fHC) able to decondense?

Answer 4

Yes

Question 5

Is HC transcriptionally active?

Answer 5

No, but euchromatin is.

Question 6

Core histone tails are post-translationally modified. Which residue is modified?

Answer 6

Lysine.

Question 7

Does HC tail acetylation loosen or tighten HC, and what is the effect of this?

Answer 7

Acetylation loosens the HC, increasing transcription.

Question 8

AcH3K9 and, interestingly, MeH3K4 are markers of what?

Answer 8

Transcription

Question 9

MeH3K9 and MeH3K27 are markers of what?

Answer 9

Heterochromatin (lack of transcription)

Question 10

As an example, H4K16 has its +ve charge neutralised when acetylated. What effect does this have?

Answer 10

Electrostatic interactions between H4 and adjacent nucleosome H2 are interrupted, as well as modulating interactions with decondensation proteins.

Question 11

MeH3K9 is recognised by which protein domain?

Answer 11

The chromodomain.

Question 12

Which protein binds to MeH3K9 to promote HC formation?

Answer 12

HP1

Question 13

HP1 also has a chromoshadow domain. What does this do?

Answer 13

The CSD allows protein/protein interactions with other proteins that have CSDs.

Question 14

What does ChIP stand for?

Answer 14

Chromatin Immunoprecipitation