Membrane and soluble secretory proteins synthesized on the rough ER undergo four principal modifications before they reach their final destinations: 

(1) Glycosylation in the ER and Golgi complex

(2) Formation of disulfide bonds in the ER

(3) Proper folding of polypeptide chains and assembly of multisubunit proteins in the ER

(4) Specific proteolytic cleavages in the ER, Golgi complex, and secretory vesicles

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#Unit 2. Cellular Organization

Two major classes of actin-nucleating proteins:

1. Formins nucleate the assembly of unbranched filaments 

2. Arp2/3 complex nucleates the assembly of branched actin networks

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#Unit 2. Cellular Organization

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#Unit 2. Cellular Organization

formin family members have two adjacent domains:

FH1- rich in proline, landing site for profilin–ATP–G-actin

FH2 - form a dimer and nucleate filament assembly

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#Unit 2. Cellular Organization

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#Unit 2. Cellular Organization

Formins are activated by membrane-bound Rho-GTP, a Ras-related small GTPase

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#Unit 2. Cellular Organization

To nucleate the assembly of branched actin filaments, Arp2/3 needs to be activated by a nucleation promoting factor (NPF)