【单选题】Definition of MTOCs (microtubule organizing center )
A.
It is a major site in which t he γ-tubulin s combine with several other associated proteins to act as a scaffold for α - β tubulin dimers during the nucleation process .
B.
It is a cytoskeletal component composed of a family of related proteins sharing common structural and sequence features , which are cytoplasmic and nuclear localization .
C.
It is composed of a double-helical polymer of the protein actin, and play s a key role in virtually all types of contractility and motility within cells.
D.
It comprise s a superfamily of ATP -dependent motor proteins which are responsible for actin -based motility.