Spc29p is a component of the Spc110p subcomplex and is essential for spindle pole body duplication

In yeast, microtubules are organized by the spindle pole body (SPB), The SP B is a disk-like multilayered structure that is embedded in the nuclear env elope via its central plaque, whereas the outer and inner plaques are expos ed to the cytoplasm and nucleoplasm, respectively. How the SPB assembles is poorly understood. We show that the inner/central plaque is composed of a stable SPE subcomplex, containing the gamma-tubulin complex-binding protein Spc110p, calmodulin, Spc42p, and Spc29p. Spc29p acts as a linker between t he central plaque component Spc42p and the inner plaque protein Spc110p, Ev idence is provided that the calmodulin-binding site of Spc110p influences t he binding of Spc29p to Spc110p, Spc42p also was identified as a component of a cytoplasmic SPB subcomplex containing Spc94p/Nud1p, Cnm67p, and Spc42p , Spc29p and Spc42p may be part of a critical interface of nucleoplasmic an d cytoplasmic assembled SPB subcomplexes that form during SPB duplication. In agreement with this, overexpressed Spc29p was found to be a nuclear prot ein, whereas Spc42p is cytoplasmic, In addition, an essential function of S PC29 during SPB assembly is indicated by the SPB duplication defect of cond itional lethal spc29(ts) cells and by the genetic interaction of SPC29 with CDC31 and KAR1, two genes that are involved in SPB duplication.