Topic 4-1

1. Topic 4-1 1

2. Topic 4-1 2 Major components An apparent amorphous mass enclosed by a nuclear envelope Within: Chromosomes Chromatin Nuclear matrix Fibrillar network Nucleoli r-RNA and ribosomes Nucleoplasm Fluid of the nucleus

3. Topic 4-1 3 The nuclear envelope Components: Two cellular membranes Barrier to ions, solutes, macromolecules Membranes fused to form pores Complex assemblies of proteins Outer membrane Ribosomes Continuous with RER

4. Topic 4-1 4 The nuclear envelope Components: Inner membrane Bound to nuclear lamina Filamentous network Nuclear lamina Supports envelope Attachment of chromatin Nuclear lamina fibers Proteins � lamins superfamily � Intermediate filaments of cytoplasm.

5. Topic 4-1 5 The nuclear envelope Components:

6. Topic 4-1 6 The nuclear pore complex (NPC) Large numbers of proteins � synthesized in cytoplasm and transported into the nucleus RNAs manufactured in nucleus � transported to cytoplasm

7. Topic 4-1 7 The nuclear pore complex (NPC) Huge macromolecular complex Octagonal symmetry 8-fold repetition of subunits 30-50 proteins � nucleoporins Nucleoporins Symmetrical � on both cytoplasmic and nuclear sides

8. Topic 4-1 8 The nuclear pore complex (NPC)

9. Topic 4-1 9 The nuclear pore complex (NPC) Low molecular wt solutes Diffuse freely Macromolecules Regulated Protein import to nucleus Nuclear localization signal (NLS) Best-studied � 1 or 2 sequences of +ve charged aa

10. Topic 4-1 10 The nuclear pore complex (NPC) Transport receptors � karyopherins Soluble Importins Cytoplasm to nucleus Exportins Nucleus to cytoplasm

11. Topic 4-1 11 The nuclear pore complex (NPC) Import example - nucleoplasmin Step 1. NLS � attached protein binds soluble NLS receptor NLS receptor = importin a/b Step 2. NLS transports complex to cytoplasmic filaments

12. Topic 4-1 12 Import example - nucleoplasmin

13. Topic 4-1 13 Import example � nucleoplasmin Step 3. Cytoplasmic filaments bend toward nucleus Step 4. Change in conformation of transporter

14. Topic 4-1 14 Import example � nucleoplasmin Role of the GTP-binding protein � Ran Active form � Ran-GTP Inactive form � Ran-GDP High concentration of GTP-Ran in nucleus Low concentration in cytoplasm

15. Topic 4-1 15 Import example � nucleoplasmin Role of the GTP-binding protein � Ran Low concn. in cytoplasm � accessory protein � Ran-GAP1 � converts GTP form to GDP form High concn. In nucleus � accessory protein � RCC1 � conversion of GDP form to GTP form

16. Topic 4-1 16 Import example � nucleoplasmin Step 5. Importin � NLS protein complex binds to Ran-GTP and importin dissociates

17. Topic 4-1 17 Import example � nucleoplasmin Step 6. Ran-GTP-importin b shuttled back to cytoplasm Step 7. Importin a subunit transported by an exportin

18. Topic 4-1 18 Export � RNAs Move as ribonucleoproteins (RNPs) Except t-RNA � direct transport by exportin-t Protein component contains nuclear export signal (NES) Exportins recognize NES Binds Ran-GTP � stabilizes complex Carried to cytoplasm Ran-GAP1 converts Ran-GTP to Ran-GDP

19. Topic 4-1 19 Export � RNAs