Cytoskeleton

Phosphorylation of γ-tubulin regulates microtubule organization in budding yeast. Vogel, J. et al. Dev. Cell 1, 621?631 (2001) [PubMed]

In this study, γ-tubulin ? an essential component of microtubule-organizing centres ? is found to be regulated by phosphorylation. The authors show that Tub4, the budding yeast γ-tubulin equivalent, is phosphorylated in a cell-cycle-dependent manner, phosphorylation being maximal during G1. Mutation of a tyrosine residue (Tyr445) to aspartate increases the assembly rate of microtubules, causing yeast cells to arrest before anaphase. This indicates that modification of γ-tubulin is important for regulating microtubule organization and function during the yeast cell cycle.

Reconstitution of physiological microtubule dynamics using purified components. Kinoshita, K. et al. Science 294, 1340?1343 (2001) [PubMed]

The addition and loss of αβ-tubulin dimer subunits from the ends of microtubules is required for the microtubule cytoskeleton to function effectively. Microtubules must polymerize more rapidly and move between polymerized and depolymerized states more frequently than has so far been achieved using purified tubulin in vitro. Here, Hyman and colleagues show that a three-component mixture ? a microtubule-stabilizing protein, XMAP215, a microtubule-destabilizing kinesin, XKCM1, and tubulin ? effectively recreates the characteristic behaviour of physiological microtubules.

Intraflagellar transport balances continuous turnover of outer doublet microtubules: implications for flagellar length control. Marshall, W. F. & Rosenbaum, J. L. J. Cell Biol. 155, 405?414 (2001) [PubMed]

Historically, ciliar and flagellar microtubules were considered static structures, but more recent data indicate that they do turn over. In this paper, the authors propose a model explaining how the length of flagella is controlled in the unicellular alga Chlamydomonas reinhardii. By visualizing turnover of tubulin, the authors show that microtubule polymerization takes place at the tip of the flagellum, and that it occurs through intraflagellar transport ? the anterograde movement of large protein complexes driven by kinesin-II. Polymerization is balanced by continuous depolymerization at the same location, and the resulting steady-state equilibrium probably controls the length of the flagellum.