The Nucleus

1
The Nucleus
2
Nuclear Morphology
3
Chromosome Territories

• Chromosomes occupy discrete regions of interphase
  nucleus

• Chromatin both heterochromatin and euchromatin
• Interchromasomal domain

4
Sites of RNA Synthesis and Processing

• Perichromatin fibrils gt10000 sites of Pol II
  transcription RNA processing

• Speckles Cajal bodies
• sites of storage for RNA splicing components

5
Nucleolar Subdomains

• rRNA transcription at FC/DFC boundary
• Ribosomal assembly in GCs
• RNA Pol I factors in FC

6
Nucleolar Organizing Regions (NORs)

• rDNA on chromosomes 13, 14, 15, 21 22
• Remains associated with Pol I transcription
  factors throughout mitosis

7
Nuclear Envelope
8
Nuclear Lamina

• Lamin B most prevalent
• Lamin A C differentiation specific

9
Nuclear Envelope Disassembly Reassembly During
Cell Division

• Lamins A C
• dephosphorylated
• Lamin B
• phosphorylated and demethylated
• Remain attached to NE remnants

10
Nuclear Pore Complexes

• 3000-5000 pores/nucleus
• 130 nm in diameter
• 55 nm central channel
• Mammalian pores composed of gt100 proteins
• Nucleoporins major class of pore proteins

11
Nuclear/Cytoplasmic Trafficking

• Nuclear Localization Signal NLS
• Many defined a. a. sequences
• Basic NLS very common
• Stretch of basic a.a. residues
• SV-40 T Ag PKKKRKV
• Direct import of protein into nucleus
• Nuclear Export Signal NES
• Direct export of nuclear proteins
• Critical for recycling of import factors
• Nuclear Retention Signal NRS
• Critical for retention of various RNA processing
  factors

12
Demonstration of NLS
C
E
D
F
Figure 16-13. A NLS ICAD causes specific import
into the nucleus of an ICAD-GFP fusion protein.
Panels A, C E show cells transfected with
ICAD-GFP without a NLS, panels B, C F are cells
transfected with ICAD-GFP with a NLS. A B-
Composite fluorescence image of GFP and DAPI. C
D- GFP fluorescence showing cytoplasmic
distribution of ICAD-GFP lacking a NLS (C). E
F- Nuclei stained with DAPI.
13
Demonstration of NES

• Site of injection, nuclear vs cytoplasmic, is
  indicated by position of arrow

14
Nuclear Import/Export Cycles

• Adapter importin ?
• Receptor importin ?
• Export receptor CAS
• Ran small GTPase
• RanGAP activates GTPase activity
• RanGEF exchanges GDP for GTP

15
Some Structures
16
Regulated Nuclear Localization