分子生物学sectionDppt课件.ppt

Section D
Prokaryotic and Eukaryotic Chromosome Structure
Molecular Biology Course
D1 Prokaryotic chromosome (mosome are referred to as non-histone proteins, including numerous DNA binding proteins that regulate the transcription, replication, repair and recombination of DNA.
Proteins in chromosome
1. Histones (组蛋白):
Core histones (H2A, H2B, H3 and H4):
10-20 kDa
located in the nucleosome (核小体) core octamer 八聚体 core (H2A)2(H2B)2 (H3)2 (H4)2
highly conserved in their sequences
a2
a3
a1
aN
4 helix-bundle
H3
H4
H3’
H4’
H4
H2B
H2A
H3
H4
H2B
H2A
H3
The Nucleosome
146 bp DNA 2X H3, H4, H2A, H2B
Nucleosomes and micrococcal nuclease treatment
Histone octamer 组蛋白八聚体
Nucleosome (核小体) core (核心)
Nucleosome core
146 bp, superhelical turn
Chromatosome染色小体
166 bp, 2 superhelical turn
DNA
Histone octamer
Histone H1
H1 histone (组蛋白H1):
23 kDa
Located outside of nucleosome core, bind to DNA more loosely
Less conserved in its sequence
The role of H1:
Stabilize the point at which DNA enters and leaves the nucleosome core.
C- tail of H1 (> the core histones): stabilize the DNA between the nucleosome cores.
Nucleosome (核小体) is the basic structural subunit of chromatin, consisting of ~200 bp of DNA and an octamer of histone proteins.
DNA + Histone octamer (组蛋白 八聚体) > Nucleosome core (核小体核心 146bp) > + H1 > Chromatosome (染色小体 166bp) > + linker DNA = Nucleosome (核小体) (~200 bp of DNA)
to make a Nucleosome (核小体)
3.“Beads on a string” structure
Linker DNA
<10 to > 100 bp
average 55 bp
Histone H1
Nucleosome repeat:
Core + linker DNA
Ca. 200 bp
Polynucleosome
Compaction ratio = 6
Nucleosome
30 nm fiber
Higher ordered
Left-handed helix
Six nucloesomes per turn
30 nm fiber
(30nm in diameter)
Solenoid-like
Nucleosome repeat
Core + linker DNA
ca 200 bp
Compaction ratio = 50
the 30-nm fiber (“zigzag model”)
Highest level of chromatin organization
5. looped domain structure