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Localization of maternal nanos mRNA to the posterior pole is essential for development of both the abdominal segments and primordial germ cells in the Drosophila embryo. Unlike maternal mRNAs such as bicoid and oskar that are localized by directed transport along microtubules, nanos is thought to be trapped as it swirls past the posterior pole during cytoplasmic streaming. Anchoring of nanos depends on integrity of the actin cytoskeleton and the pole plasm; other factors involved specifically in its localization have not been described to date. Here we use genetic approaches to show that the Hsp90 chaperone (encoded by Hsp83 in Drosophila) is a localization factor for two mRNAs, nanos and pgc. Other components of the pole plasm are localized normally when Hsp90 function is partially compromised, suggesting a specific role for the chaperone in localization of nanos and pgc mRNAs. Although the mechanism by which Hsp90 acts is unclear, we find that levels of the LKB1 kinase are reduced in Hsp83 mutant egg chambers and that localization of pgc (but not nos) is rescued upon overexpression of LKB 1 in such mutants. These observations suggest that LKB1 is a primary Hsp90 target for pgc localization and that other Hsp90 partners mediate localization of nos.

The quaternary structure of phosphorylase kinase (Phk) has been studied by using the photoreactive cross-linker N-5-azido-2-nitrobenzoyloxysuccinimide. Phk is an enzyme that controls glycogenolysis in skeletal muscles and is a hexadecameric oligomer by structure. Intramolecular cross-linking proceeded through the mono-derivatization of the holoenzyme with the succinimidyl group followed by the photoactivation of the covalently attached azido group. The cross-linking produced a major and a minor conjugate whose formation were significantly altered in activated conformations of the enzyme.

The dynamic instability behavior due to the cap at microtubule ends during the assempbly of microtubules is investigated. Results point out that there is no evidence for the accumulation of tubulin-GDP-phosphate subunits with nonexchangeable phosphate in microtubules. It is known that tubulin-GDP-phosphate subunits with exchangeable phosphate lead to microtubule instabilization.