Component of the kinetochore, a multiprotein complex that assembles on centromeric DNA and attaches chromosomes to spindle microtubules, mediating chromosome segregation and sister chromatid segregation during meiosis and mitosis. Component of the inner kinetochore COMA complex, which connects centromere-associated proteins and the outer kinetochore. COMA interacts with other inner kinetochore proteins to form the inner kinetochore constitutive centromere-associated network (CCAN), which serves as a structural platform for outer kinetochore assembly. Component of the heterotetrameric kinetochore subcomplex COMA, which consists of AME1, CTF19, MCM21 and OKP1 (PubMed:10323865, PubMed:14633972). The COMA subcomplex is part of a larger constitutive centromere-associated network (CCAN) (also known as central kinetochore CTF19 complex in yeast), which is composed of at least AME1, CHL4, CNN1, CTF3, CTF19, IML3, MCM16, MCM21, MCM22, MHF1, MHF2, MIF2, NKP1, NKP2, OKP1 and WIP1 (PubMed:12408861, PubMed:22561346). COMA binds the centromeric nucleosome-binding protein MIF2, and to the outer kinetochore MIND subcomplex (By similarity). CTF19 interacts with the CTF3 complex subunits CTF3, MCM16 and MCM22 as well as CHL4 and IML3 (PubMed:11782448, PubMed:12589047). Interacts with the N-terminal domain of centromeric nucleosome protein CSE4 and with the CBF3 complex subunit A (CBF2) (PubMed:10958698). Present with 1254 molecules/cell in log phase SD medium. Belongs to the CENP-P/CTF19 family.