TUB4, the gene for Saccharomyces cerevisiae gamma -Tubulin, encodes a 473 amino acid structural protein that localizes to the spindle pole body. gamma Tubulin, an essential protein for cell growth, organizes microtubule arrays in the nucleus and cytoplasm. gamma Tubulin-depleted cells fail to form functional spindles and arrest during nuclear division. gamma Tubulin associates with spindle body components Spc97 and Spc98 to form the gamma Tubulin complex. The budding yeast gamma Tubulin complex contains one molecule each of Spc97 and Spc98 and two molecules of gamma Tubulin. In the SPB, Spc110 binds Spc97 and Spc98 of the gamma Tubulin complex. 2D gel analysis indicates five isoforms of gamma Tubulin. The phosphorylation of gamma Tubulin at Tyr 445 plays a regulatory role in microtubule formation. The incidence rate for this phosphorylation event peaks during G1.