Proposed to be part of the KMN network incorporating the MIS12 complex and NDC80 complex that is required for establishing the kinetochore-microtubule interface that aids in chromosome segregation during meiotic and mitotic cell division (PubMed:14522947, PubMed:15371340, PubMed:17129783, PubMed:18070910). Appears to function downstream of hcp-3 (CENP-A) and hcp-4 (CENP-C) in the kinetochore assembly hierarchy (PubMed:15767665, PubMed:16273096). Has a role in the correct localization of the spindly-like protein spdl-1 and the RZZ complex that is composed of rod-1, czw-1 and zwl-1 to kinetochores (PubMed:18765790, PubMed:18936247). Required for the recruitment of spindle-assembly checkpoint components bub-1 and mdf-1/2 to unattached kinetochores (PubMed:19109417, PubMed:20729837, PubMed:24567362). Interacts with hcp-3 and hcp-4 to form a complex (PubMed:14522947). Interacts with hcp-4, him-10, kbp-3, kbp-4, kbp-5, knl-3, and ndc-80 (PubMed:15371340). Interacts with kbp-1, kbp-2 and mis-12; which make up the MIS12 complex (PubMed:17129783). Also found on the surface of chromosomes (PubMed:14522947). Subcellular localization dependent on expression of hcp-3, hcp-4, knl-3 and knl-2 (PubMed:14522947, PubMed:15371340, PubMed:16273096, PubMed:17339379). During anaphase of meiosis I, localized also to spindle-associated rod-shaped structures which depends on zwl-1 (PubMed:20729837). Expressed on chromosomes from early prophase until late anaphase. The N-terminus contains a number of repeats which contribute additively to bub-1 recruitment to unattached kinetochores. The repeats are not required for localization to kinetochores. Perturbed spindle-kinetochore interactions, segregation defects and premature spindle elongation (PubMed:14522947, PubMed:15767665, PubMed:18070910). RNAi-mediated knockdown results in reduced localization of the spindly-like protein spdl-1 and the RZZ complex component zwl-1 to kinetochores (PubMed:18765790, PubMed:18936247). Does not affect spdl-1 localization to microtubules (PubMed:18936247).