Cell Biology Lecture #28 Compartmentalization and nuclear transport p.551-568

Nucleus = 10 billion proteins of 10,000 different kinds, made in cytosol selectively imported.

(Why is "proteomics" such a hot area?)

How are all of these proteins sorted? Answer: we don't know everything, but we do know some things.

Nucleus, cytosol, rough and smooth ER, Golgi, mitochondria, lysosomes, peroxisomes, endosomes. Notice percentages, p.553 liver hepatocyte

Plasma membrane minor membrane for most eucaryotes. Microtubules hold membrane-enclosed organelles where they need to be. Surface area/volume for procaryotes and eucaryotes

Coalesced proteins in procaryotes = specialization similar to organellar. Default "sorting signal of proteins = cytosol.

5 compartments: 1.nucleus+cytosol 2.secretory and endocytic vesicles 3. Mitochondria 4.plastids 5.peroxisomes. NOT A BAD DAILY QUIZ QUESTION!

3 sorting methods:(red, blue, green of fig. 12-7)

1. Nuclear pores = selective "gates"

2. Protein translocators

3. Vesicular transport.

Signal peptide = cut out(end of a.a. chain);signal patch = remains (Golgi to lysosomes, reimport)

Why is transfection used to evaluate signal sequences?

Panel 12-1: Experimental approaches. Ts mutants. Epigenetic information.

Ribosomes studding nuclear membrane make proteins sent to perinuclear space. Nuclear pore complex= critical import, export function.

Inject nuclear proteins, various sized molecules, altered proteins with T-antigen signal into cytosol, coat gold particle, see if imported to nucleus, or how treated. Nuclear localization signals=short (T antigen of SV-40 is 8). Pores bidirectional. Transport fully folded proteins

Nuclear lamina disperse, then repolymerize on chromosomal surfaces (phosphorylation and rephosphorylation of lamins drives these processes). Nuclear localization signals not cleaved off, unlike other compartments' proteins.

Great way to control gene regulatory proteins and processing in nucleus: Don't let protein leave compartment until wanted (or, signalled).