Centrosomes function as the major microtubule (MT)-organizing center. They are composed of a pair of centrioles which are surrounded by the pericentriolar material. Here, we describe the molecular characterization of a novel protein, named centlein (centrosomal protein). Centlem was a protein of 721 amino acids with a calculated molecular weight of 82,717 and possessed coiled-coil domains. Western blot analysis indicated that centlein was ubiquitously expressed. Endogenous centlein as well as enhanced green fluorescent protein-fused centlein was localized at centrosomes in interphase and mitosis. When centrosomes were isolated from cells treated with nocodazole, an MT-disrupting agent, centlein and the centrosomal protein, gamma-tubulin, were enriched in the same fractions. These data indicate that centlein is a widespread centrosomal protein and that its association with centrosomes is independent of MTs. Centlein appeared to be enriched in the mother centriole in G1 phase, suggesting possible involvement of centlein in mother-centriole-related functions, such as duplication of centrioles and generation of primary cilia. (c) 2007 Elsevier Inc. All rights reserved.