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Chromosome Territories• Chromosomes occupy
discrete regions of interphase nucleus
• Chromatin – both heterochromatin and euchromatin
• Interchromasomal domain
Sites of RNA Synthesis and Processing
• Perichromatin fibrils – >10000 sites of Pol II transcription & RNA processing
• Speckles & Cajal bodies– sites of
storage for RNA splicing components
Nucleolar Subdomains
• rRNA transcription at FC/DFC boundary
• Ribosomal assembly in GCs
• RNA Pol I & factors in FC
Nucleolar Organizing Regions (NORs)
• rDNA on chromosomes 13, 14, 15, 21 & 22
• Remains associated with Pol I & transcription factors throughout mitosis
Nuclear Envelope Disassembly & Reassembly During Cell Division
• Lamins A & C – dephosphorylated
• Lamin B – phosphorylated and
demethylated– Remain attached to
NE remnants
Nuclear Pore Complexes
• ~ 3000-5000 pores/nucleus
• 130 nm in diameter• 55 nm central channel• Mammalian pores
composed of >100 proteins
• Nucleoporins major class of pore proteins
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
Demonstration of NLS
C
D
E
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.
Nuclear Import/Export
Cycles• Adapter = importin • Receptor = importin • Export receptor = CAS
• Ran – small GTPase• RanGAP – activates
GTPase activity• RanGEF – exchanges
GDP for GTP