Basic assembly features of cytoskeletal filaments
| Properties | IFs | Microtubules | Actin filaments |
| Assembly units | Apolar fibrous tetramers | Globular heterodimers | Globular monomers |
| Nucleotide requirement | None | GTP | ATP |
| Nucleation sites/nucleating factors | Cell periphery/unknown | Microtubule organizing center (MTOC)/γ-tubulin ring complex | Juxtamembranous sites/ARP2/3 complex, formins |
| Elongation | Both ends | Plus end | “Barbed” end |
| Protofilaments | 8 | 13-15 | Double helix |
| Filament diameter | 10 nm | 25 nm | 6 nm |
| Preferred disassembly site | Unknown | Minus end | “Pointed” end |
| Network remodeling | Lateral subunit exchange/network cycling | Dynamic instability/treadmilling | Retrograde flow/treadmilling |
| Properties | IFs | Microtubules | Actin filaments |
| Assembly units | Apolar fibrous tetramers | Globular heterodimers | Globular monomers |
| Nucleotide requirement | None | GTP | ATP |
| Nucleation sites/nucleating factors | Cell periphery/unknown | Microtubule organizing center (MTOC)/γ-tubulin ring complex | Juxtamembranous sites/ARP2/3 complex, formins |
| Elongation | Both ends | Plus end | “Barbed” end |
| Protofilaments | 8 | 13-15 | Double helix |
| Filament diameter | 10 nm | 25 nm | 6 nm |
| Preferred disassembly site | Unknown | Minus end | “Pointed” end |
| Network remodeling | Lateral subunit exchange/network cycling | Dynamic instability/treadmilling | Retrograde flow/treadmilling |
The table summarizes textbook knowledge integrating also recent results on keratins. For further reading see, e.g., Chhabra and Higgs (2007), Herrmann et al. (2007), Akhmanova and Steinmetz (2008), Wade (2009); Campellone and Welch (2010).