Fig. 6. Schematic diagrams of TuRC recruitment to interphase centrosomes, mitotic centrosomes during centrosome maturation, and to mitotic spindle MTs. (A) During interphase, centrosomal -tubulin is exchanged with the cytoplasmic pool. (B) Additional TuRC is recruited to centrosomes as cells enter mitosis in a process called centrosome maturation. During centrosome maturation, the interphase centrosome increases in size and recruits five times more -tubulin. Concomitantly, five times more MTs are nucleated by the mature centrosomes. (C) During mitosis, TuRC is recruited to centrosomes as well as to spindle MTs (indicated by arrows; notice that TuRC is not drawn to scale). How -tubulin is recruited to different sites and in a cell-cycle-dependent manner is only beginning to emerge. The mechanisms of TuRC recruitment to centrosomes during interphase and mitosis are probably mediated by distinct sets of proteins (e.g. Casenghi et al., 2003).