kinetochór

Kinetochór is a protein structure located at the centromere of a chromosome that serves as the attachment site for spindle microtubules during cell division, enabling chromosome movement and segregation. It is a multi-subunit complex organized into functional regions that interact with centromeric chromatin and with microtubules.

The kinetochór comprises an inner kinetochore assembled on centromeric chromatin containing CENP-A–containing nucleosomes, and an outer kinetochore that interfaces with microtubules. The inner kinetochore includes CCAN components such as CENP-C and CENP-T that recognize and bind centromeric chromatin. The outer kinetochore contains the KMN network (KNL1 complex, Mis12 complex, and Ndc80 complex), which provides the principal microtubule-binding interface and coordinates attachment stability and force transmission. Additional factors, including dynein and various regulatory proteins, contribute to the dynamic regulation of attachment.

During mitosis and meiosis, the kinetochór mediates bi-orientation by attaching sister kinetochores to microtubules from opposite spindle poles. Microtubule dynamics generate pulling forces as plus ends shorten, moving chromosomes toward poles while maintaining tension that stabilizes correct attachments. The kinetochór also participates in the spindle assembly checkpoint: unattached kinetochores recruit checkpoint proteins (e.g., Mps1, BUBR1/BUB3, MAD1/MAD2) to delay anaphase until proper attachments form. Tension across sister kinetochores helps silence the checkpoint, a process regulated by kinases such as Aurora B.

Across eukaryotes, kinetochors vary in composition and size; some organisms have holocentric kinetochores that assemble along the chromosome length rather than at a single centromere.