LPC: 10 mg/ml leupeptin,10 mg/ml pepstatin A, and 10 mg/ml chymostatin dissolved in DMSO. a role for Dgrip84 in regulating the activity and/or the location of the -tubulin complexes formed with Tub23C. INTRODUCTION The temporal and spatial control of microtubule nucleation and organization are essential for many fundamental cellular processes, including cell shape changes, intracellular transport, cell motility, partitioning of polarity signals during embryonic development, and, perhaps most importantly, the faithful segregation of chromosomes during cell division. In most animal cells, microtubules are nucleated and organized by the centrosome, which is composed of a pair of centrioles surrounded by the amorphous pericentriolar material (PCM) that appears to be the site of microtubule nucleation and anchoring (Gould and Borisy, 1977 ). Although efforts to generate an inventory of centrosomal components have made great progress in recent years (for example, Andersen lacking endogenous -tubulin (Horio and Oakley, 1994 ), suggesting that -tubulins are functionally conserved in phylogenetically distant organisms. Within PIK-294 the cell, -tubulin exists in a multiprotein complex containing between two (in the case of eggs or embryos appear ring-shaped and have therefore been named -tubulin ring complex (TuRC; Zheng (Knop and Schiebel, 1997 ), where it may be the only soluble -tubulin complex. The metazoan TuRC is Sema3a thought to be composed of six or seven tetramers held together and capped by several additional proteins that copurify with -tubulin from egg extracts PIK-294 or embryos (Zheng according to its location on the genetic map) is highly expressed in the PIK-294 ovary and is deposited in the egg, where it is thought to orchestrate the early embryonic cleavages (Wilson results in female sterility (Tavosanis is essentially ubiquitous and is required for viability, microtubule organization during somatic mitotic divisions, and male meiosis (Sunkel is detected at centrosomes in syncytial embryos, whereas punctate structures containing distribute throughout the cytoplasm (Wilson and localize to centrosomes in cellularized embryos (Tavosanis tissue culture cells (Raynaud-Messina have been reported to vary only slightly throughout the cell cycle, whereas centrosomal levels increased sharply during late G2. Furthermore, was also recruited to the microtubules of the mitotic spindle, whereas was never found on spindle microtubules. This suggests the existence of mechanisms that allow the cell to distinguish between the two -tubulin isotypes. Here, we set out to gain a better understanding of the biochemistry of isolated from tissue culture cells forms bona fide ring complexes that include most of the same Grips as the TuRCs formed by and associate with distinct splice variants of Dgrip84/GCP2 that differ by 74 amino acids in their amino termini. We speculate that Dgrip84 may be involved in regulating the subcellular localization of -tubulin. MATERIALS AND METHODS Buffers and Reagents The following buffers were used: HB: 50 mM K-HEPES, pH 7.6, 1 mM MgCl2, 1 mM EGTA, 1 mM -mercaptoethanol (-ME) and protease inhibitor stock (1:200 final dilution; see below). H100: HB plus 100 mM NaCl; H200: HB plus 200 mM NaCl; and H500: HB plus 500 mM NaCl. Elution buffer (EB): H200 plus 100 M GTP and 1 mg/ml Dros23C or Dros37C peptide. Homogenization buffer (for embryos): H100 plus 10%glycerol, 1 mM PMSF and protease inhibitor stock (1:100 final dilution). Cell lysis buffer (for S2 and Kc cells): H200 plus 0.5% NP-40, 1 mM GTP, and 1 mM PMSF. Protease inhibitor stock: 10 mM benzamidine-HCl, 1 mg/ml aprotinin, 1 mg/ml leupeptin, and 1 mg/ml pepstatin A in ethanol. LPC: 10 mg/ml leupeptin,10 mg/ml pepstatin A, and 10 mg/ml chymostatin dissolved in DMSO. Mounting medium: 20 mM Tris-Cl, pH 9.0, 90% glycerol, and 0.1% (1999) . Synthetic peptides (made by the Protein Synthesis facility of the University of Wisconsin, Madison Biotech Center) corresponding to the COOH-terminal 17 amino acids of (Cys-PVDSKSEDSRSVTSAGS; GenBank Accession no. “type”:”entrez-protein”,”attrs”:”text”:”P23257″,”term_id”:”45644955″,”term_text”:”P23257″P23257) or (Cys-QIDYPQWSPAVEASKAG; GenBank Accession no. “type”:”entrez-protein”,”attrs”:”text”:”P42271″,”term_id”:”45644999″,”term_text”:”P42271″P42271) were used to raise and affinity purify rabbit polyclonal antibodies as described elsewhere (Field medium as described by the supplier (Invitrogen, Carlsbad, CA). Cells to be used for extract preparation were grown for 4 d at 27C in 70 ml medium in T-150 flasks. Cells were collected by centrifugation and washed twice with PBS, the volume of the cell pellet was estimated, and the cells were stored at ?80C until use. PEG Precipitation PEG (polyethylene glycol P-2139; average mol wt 5C8000; Sigma Chemical Co., St. Louis,.