The nucleus

Role of the nucleus

Maintain the integrity of the DNA and controls cell activity thru regulating gene expression. Mediates the replication of DNA during the cell cycle

separates nuclear and cytosolic enzymes (harsh environ)

separates transc and transl

what are the main structures of the nucleus

nuclear envelope - double memb

nuclear membrane - 2 make up the envelope (inner and outer) selective permeability NPC

nuclear lamina - meshwork prov mechanical support

what are subnuclear bodies

made of proteins, rna and parts of chromosome

have multiple roles

not membrane bound

what contacts the nuclear envelope

ER is continuous with outer memb

Inner memb is associated with the nuclear lamina (proteins of the memb assoc with it)aht

what is the nuclear lamina

network of intermediate filaments (fibrillar)

has memb assoc proteins

regulates DNA rep and cell division

chromatin organisation

anchors NPCand maintains nuclear shape.

prov structural support

what are laminopathies

muts in genes encoding the nuclear lamina (contain lamin A/C proteins)

what are main causes of laminopathies

muts in Lamin A/C proteins or lamina assoc proteins

what are the effects in laminopathies

defects in filament assembily

filament attachment to envelopeand disruption of nuclear shape, leading to various cellular dysfunctions and diseases.

what are main tissues affected by laminopathies

physically stressed tissues (muscle fibres, bone, skin, connective tissue)

what is the treatmetn for laminopathies

no cure, just treat symptoms

symptoms of Emery-Dreifuss muscular dystrophy

skeletal and cardiac muscle affected (electrical signal abnormalities/conduction defects)

progressive muscle weakening and wasting (impair movement)

what is HGPS (Hutchinson-Gilford progeria syndrome)

Accelerated symptoms of ageing

point mut in LMNA gene

cause transl of Lamin A protein lacking 50 aa’s

waht affect does the 50 aa short Lamin A have

incorporated abnormally into lamina

cause mechanical defects

lamina thickens

lose peripheral chromatin

more DNA damage

what are chromosome territories

discrete individual patches of DNA (organises itself into them)

euchromatin

beads on a string (histones wrap DNA) actively transcribed

heterochromatin

histones wrap into 30 nm fibre

most compact

constitutively expressed

constitutive heterochromatin vs facultative heterochromatin

never expressed, differentially expressed

what organises the chromatin fibre in the nucleus into separate compartments of higher order structure

insulator elements (form loops of DNA that anchor to nuclear periphery via lamina)

what goes thru NPC (multiprotein assembily)

<40 kDa proteins freely perm

larger mols translocated via active mechanism that req transport factors

NPC structure

octagonally (8 protein ring) organised symmetric cylider

in envelope

channel can expand and contract

made of 30-50 nucleoporins

ring of 8 proteins at either end

8 filaments on each emanate into cyto or nucleus hwo

how proteins tranlocated into nucleus via NPC

proteins with Nuc Localisation Signal (NLS) recognised by an importin bound by Ran-GDP

importin binds filaments of NPC

sequential binding thru pore

Nuc Guanine nucleotide exchange factor (GEF) exchanges GDP on Ran to GTP cause protein to released

Importin/Ran-GTP complex exported

GTPase activating protein (GAP) in cyto hydolyses GTP to GTP

Importin alpha structure

has 2 NLS binding sites

a monopartite NLS binds 1 site

a bipartite NLS binds both sites

consensus seq has lot of K and R. Bipartite consensus seq obvs longer (2 seqs sep by 10-12 aas) bind helix 3

nuclear export

have nuc export signals (NES), lot of L

recognised by exportins in presence of Ran-GTP

transp thru NPC via sequential binding

in cyto GTP hydrolysis cause dissoc of proteinwhata

what are importins and exportins

receptors

result of diseases linked to NPC

accumulation of materials in or outside of nucleus name (often mut in Nup214, binds NES therefore accum in nuc)

Triple A syndrome (Achalasia-Addisonianism-Alacrimia syndrome)

lack of accumulation of ALADIN into the NPC (cant get into nuc, proteins involved in dna protect and repair therefore damage accumulates)

How do some viruses use the NPC

can have NLS

bind to importins (have NLSs) and cross NPC

or large viruses dock on NPC and release DNA contents into nuc

how does mRNA exit the nucleus

processed mRNA has diff proteins assoc than pre-mRNA and is stabilised by protein binding, therefore export competent

what is the shape seen when mRNA is exported from nucleus

Dumbbell shape, then ribosomes assoc with it

what is hTREX and waht are muts in it linked with

a transcription/export complex (where newly transc mRNA comes out of ribo)hwo

Stabilises and assists in export of mRNA

cancers have abnormal hTREX

what does hTREX mut do

enhance formation of R loops

DNA/newly syth RNA binding as no hTREX to deliver it away from unwound DNA chain

R loops halts transc therefore poss for DNA damage