Abstract
The two yeast proteins Mlp1p and Mlp2p (homologues of the vertebrate protein Tpr) are filamentous proteins attached to the nuclear face of nuclear pore complexes. Here we perform a proteomic analysis, which reveals that the two Mlps have strikingly different interacting partners, testifying to their different roles within the cell. We find that Mlp2p binds directly to Spc110p, Spc42p, and Spc29p, which are three core components of the spindle pole body (SPB), the nuclear envelope-associated yeast spindle organizer. We further show that SPB function is compromised in mlp2 mutants. Cells lacking Mlp2p form significantly smaller SPBs, accumulate aberrant SPB component-containing structures inside the nucleus, and have stochastic failures of cell division. In addition, depletion of Mlp2p is synthetically lethal with mutants impaired in SPB assembly. Based on these data, we propose that Mlp2p links the SPB to the peripheral Mlp assembly, and that this linkage is required for efficient incorporation of components into the SPB.