IN-VITRO RECONSTITUTION OF CENTROSOME ASSEMBLY AND FUNCTION - THE CENTRAL ROLE OF GAMMA-TUBULIN

The centrosome nucleates microtubule polymerization, affecting microtu bule number, polarity, and structure. We use an in vitro system based on extracts of Xenopus eggs to examine the role of gamma-tubulin in ce ntrosome assembly and function. gamma-Tubulin is present in the cytopl asm of frog eggs and vertebrate somatic cells in a large similar to 25 S complex. The egg extracts assemble centrosomes around sperm centriol es. Formation of a centrosome in the extract requires both the gamma-t ubulin complex and ATP and can take place in the absence of microtubul es. gamma-Tubulin is not present on the sperm prior to incubation in e xtract, but is recruited from the cytoplasm during centrosome assembly . The gamma-tubulin complex also binds to microtubules, likely the min us end, independent of the centrosome. These results suggest that gamm a-tubulin is an essential component of the link between the centrosome and the microtubule, probably playing a direct role in microtubule nu cleation.