Proteins That Control Microtubule Location

The smaller proteins Stu2p from Saccharomyces cerevisiae and Alpl4 and Disl from Schizosaccharomyces pombe, which are homologous to XMAP215, 

At the start of mitosis, this family of proteins is important in organizing spindle poles. In Drosophila, for example, Msps (mini-spindles) interacts via its C-terminal with D-TACC (the Drosophila transforming acidic coiled-coil-contabling ) protein (Lee et al., 2001). This and other members of the family interact, directly or indirectly, with a wide variety of other proteins (Ohkura et al., 2001). 

Orbit/MAST proteins, also known as CLIP-associated proteins (CLASPs), are involved in the regulation of microtubule dynamics and bind to microtubule plus ends via CLIP115 or CLIP170. Active CLASP suppresses microtubule assembly and axon outgrowth (Lee et al., 2004), whereas activated adenomatous polyposis coli protein (APC see below) promotes microtubule assembly and axon outgrowth. 

The Hook family of proteins resembles CLIPs in that they consist predominantly of coiled-coil. However, the N-terminal domains, which attach to microtubules, differ in sequence from other known microtubulebinding domains. The C-terminal domains are adapted to bind specifically to particular organelles. Hook3, for example, appears to play a role in defining the architecture and localization of the mammalian Golgi complex (Walenta et al., 2001). This helps to explain why the integrity of the Golgi complex is completely dependent on the presence of the microtubule network. 

is supported by an award from the Leverhulme Trust to Dr Jan Lowe, whom we also thank for inspiring discussions. 

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Nanos protein localization in the posterior embryo is intimately coupled to the regulation of translation of nanos mRNA. The nanos mRNA that is not located at the posterior is not translated due to a protein called Smaug that binds the 3 UTR of nanos mRNA. Localization of nanos mRNA at the posterior depends on other proteins as well. One of these is Oskar, whose maternally provided mRNA is transported to the posterior by kinesin, a motor protein that moves along microtubules (Chapter 20). Therefore the kinesin controls, after several intervening steps, the localized activity of a transcription factor (Hunchback). 

In all eukaryotes, three components participate in attaching chromosomes to microtubules the centromere, kinetochore and spindle proteins, and the cell-cycle machinery. The location of the centromere and hence that of the kinetochore Is directly controlled by a specific sequence of chromosomal DNA termed centromeric DNA (Chapter 10). Although the sequences of centromeric DNA and of DNA-binding proteins In the kinetochore are not well conserved through evolution, the cell-cycle proteins and many of the... 

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