Ska3, also designated C13orf3 or RAMA1, is a 412 amino acid protein that belongs to the RAMA1 family of proteins. A component of the SKA1 complex, Ska3 localizes to the outer kinetochore and spindle microtubules during mito- sis. The SKA1 complex is a microtubule-binding subcomplex of the outer kine- tochore and is composed of two Ska1-Ska2 heterodimers, each heterodimer interacting with a Ska3 homodimer . Within the complex, which is important for chromosome segregation and facilitates microsphere movement along microtubules, Ska3 acts as a mediator of microtubule-stimulated oligomeriza- tion. The gene encoding for Ska3 maps to chromosome 13. Comprising nearly 4% of human DNA, chromosome 13 contains around 114 million base pairs and 400 genes. Key tumor suppressor genes on chromosome 13 include the breast cancer susceptibility gene, BRCA2, and the RB1 (retinoblastoma) gene. RB1 encodes a crucial tumor suppressor protein which, when defective, leads to malignant growth in the retina and has been implicated in a variety of other cancers. The gene SLITRK1, which is associated with Tourette syndrome, is on chromosome 13. As with most chromosomes, polysomy of part or all of chro- mosome 13 is deleterious to development and decreases the odds of survival. Trisomy 13, also known as Patau syndrome, is quite deadly and the few who survive past one year suffer from permanent neurologic defects, difficulty eating and vulnerability to serious respiratory infections.
