The Saccharomyces cerevisiae nuclear membrane is part of a complex nuclear envelope environment also containing chromatin, integral and peripheral membrane proteins, and large structures such as nuclear pore complexes (NPCs) and the spindle pole body. To study how properties of the nuclear membrane affect nuclear envelope processes, we altered the nuclear membrane by deleting the SPO7 gene. We found that spo7Δ cells were sickened by the mutation of genes coding for spindle pole body components and that spo7Δ was synthetically lethal with mutations in the SUN domain gene MPS3. Mps3p is required for spindle pole body duplication and for a variety of other nuclear envelope processes. In spo7Δ cells, the spindle pole body defect of mps3 mutants was exacerbated, suggesting that nuclear membrane composition affects spindle pole body function. The synthetic lethality between spo7Δ and mps3 mutants was suppressed by deletion of specific nucleoporin genes. In fact, these gene deletions bypassed the requirement for Mps3p entirely, suggesting that under certain conditions spindle pole body duplication can occur via an Mps3p-independent pathway. These data point to an antagonistic relationship between nuclear pore complexes and the spindle pole body. We propose a model whereby nuclear pore complexes either compete with the spindle pole body for insertion into the nuclear membrane or affect spindle pole body duplication by altering the nuclear envelope environment.
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