Nucleus . Chromosome, centromere . Chromosome, centromere, kinetochore . Assembly of CENPS and CENPX and its partner subunits CENPT and CENPW at centromeres occurs through a dynamic exchange mechanism. Although exchange is continuous in the cell cycle, de novo assembly starts principally during mid-late S phase and is complete by G2. CENPX being less stably bound at the kinetochore than CENPS. .