Actin exists as: 

a globular monomer -G-actin 

a filamentous polymer- F-actin

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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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Filament capping proteins:

CapZ blocks (+)end Tropomodulin blocks (-)end

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