ROCKs (ROCK1 and ROCK2) occur in mammals (human, rat, mouse, cow), zebrafish, Xenopus, invertebrates (C. elegans, mosquito, Drosophila) and chicken.

Human ROCK1 has a molecular mass of 158 kDa and is a major downstream effector of the small GTPase RhoA.

Mammalian ROCK consists of a kinase domain, a coiled-coil region and a Pleckstrin homology (PH) domain, which reduces the kinase activity of ROCKs by an autoinhibitory intramolecular fold if RhoA-GTP is not present.

[1][2] Rat ROCKs were discovered as the first effectors of Rho and they induce the formation of stress fibers and focal adhesions by phosphorylating MLC (myosin light chain).

ROCK is a key regulator of actin organization and thus a regulator of cell migration as follows: Different substrates can be phosphorylated by ROCKs, including LIM kinase, myosin light chain (MLC) and MLC phosphatase.

[2][6] ROCK also regulates cell migration by promoting cellular contraction and thus cell-substratum contacts.

ROCK increases the activity of the motor protein myosin II by two different mechanisms: Thus in both cases, ROCK activation by Rho induces the formation of actin stress fibers, actin filament bundles of opposing polarity, containing myosin II, tropomyosin, caldesmon and MLC-kinase, and consequently of focal contacts, which are immature integrin-based adhesion points with the extracellular substrate.

ROCK can also be regulated by lipids, in particular arachidonic acid, and protein oligomerization, which induces N-terminal transphosphorylation.