Chapter 8 Chromatin Begriffe

Question 1

nucleosome

Answer 1

The basic structural subunit of chromatin, consisting of about 200 bp of DNA and an octamer of histone proteins.

Question 2

histone tails

Answer 2

Flexible amino- or carboxy-terminal regions of the core histones that extend beyond the surface of the nucleosome.
Histone tails are sites of extensive posttranslational
modification.

Question 3

10 nm fiber

Answer 3

A linear array of nucleosomes generated by unfolding from the natural condition of chromatin.

Question 4

30 nm fiber

Answer 4

A coil of nucleosomes. It is the basic level of organization of nucleosomes in chromatin.

Question 5

MNase

Answer 5

cleaves linker DNA and releases individual nucleosomes from chromatin

Question 6

Linker DNA

Answer 6

region of 7 to 115 bp that is susceptible to early cleavage by nucleases

Question 7

linker histones

Answer 7

A family of histones (such as histone H1) that are not components of the nucleosome core.
– Linker histones bind nucleosomes and/or linker DNA and promote 30 nm fiber formation.

Question 8

nonhistone

Answer 8

Any structural protein found in a chromosome except one of the histones.

Question 9

Histones are modified by

Answer 9

methylation
acetylation,
phosphorylation
ubiquitylation
sumoylation
ADPribosylation, and others

Question 10

histone code hypothesis

Answer 10

Combinations of specific histone modifications define the function of local regions of chromatin

Question 11

How do histone posttranslational modifications affect the chromatin?

Answer 11

Model 1: Chromatin sturctural change (Acetylation, phosphorylation)
Model 2: inhibit binding of negativ activating factor H3S10 phosphorylation occludes HP1 binding at H3K9me
Model 3: recruit positive activating factor (HP1 binds H3K9me through; Its chromodomain)

Question 12

Writing, erasing and reading of histone modifications

Answer 12

Wiring: kinase, acetylase and methylase

erasing: phosphatase, de-acetylase and de-methylase
reading: Bromodomain, Chromodomain, PHD-Finger Domain

Question 13

Histone variants

Answer 13

H1-H3 are members of related variant family
Histone variants can be closely related to or highly divergent from canonical histones.
Different variants serve different functions in the cell.

Question 14

When is Chromatin assembly required?

Answer 14

During
• Replication
• Transcription
• DNA repair

Question 15

How to determine nucleosome occupancy and positioning?

Answer 15

• DNAseI hypersensitivity
• Mnase hypersensitivity
• ChIP with histone antibodies

Question 16

What determines the positioning of

nucleosomes?

Answer 16

• DNA sequence
• ATP-dependent nucleosome remodeling enzymes
• Transcription factors (specific activators, preinitiation complex, elongating RNA polymerase II)
• Nucleosome positioning gene expression