Differential properties of the two Drosophila gamma-tubulin isotypes

The functional significance of distinct gamma -tubulins in several unrelate d eukaryotes remains an enigma due to the difficulties to investigate this question experimentally. Using specific nucleotidic and immunological probe s, we have demonstrated that the two divergent Drosophila gamma -tubulins, gamma -tub23C and gamma -tub37CD, are expressed in cultured cells. gamma -t ub37CD is constantly detected at the centrosome and absent in the mitotic s pindle, while gamma -tub23C is extensively recruited to the centrosome duri ng mitosis and relocalizes in the mitotic spindle. The two gamma -tubulins exhibit distinct biochemical properties. gamma -tub23C is present in the so luble gamma -tubulin small complexes (10S) and gamma -tubulin big complexes (35S) and is loosely associated to the cytoskeleton. In contrast, gamma -t ub37CD is undetectable in the soluble fraction and exhibits a tight binding to the centrosome. Syncytial embryos also contain the two gamma -tubulin i sotypes, which are differentially recruited at the centrosome. gamma -tub23 C is present in the 10S soluble complexes only, while gamma -tub37CD is con tained in the two soluble complexes and is recruited at the centrosome wher e it exhibits an heterogeneous binding. These results demonstrated an heter ogeneity of the two Drosophila gamma -tubulin isotypes both in the cytoskel etal and the soluble fractions. They suggest the direct implication of the 35S complex in the centrosomal recruitment of gamma -tubulin and a conditio nal functional redundancy between the two gamma -tubulins.