Localization of the 26S proteasome during mitosis and meiosis in fission yeast

The 26S proteasome is a large multisubunit complex involved in degrading bo th cytoplasmic and nuclear proteins. We have investigated the localization of this complex in the fission yeast, Schizosaccharomyces pombe. Immunofluo rescence microscopy shows a striking localization pattern whereby the prote asome is found predominantly at the nuclear periphery, both in interphase a nd throughout mitosis. Electron microscopic analysis revealed a concentrati on of label near the inner side of the nuclear envelope. The localization o f green fluorescent protein (GFP)-tagged 26S proteasomes was analyzed in li ve cells during mitosis and meiosis. Throughout mitosis the proteasome rema ined predominantly at the nuclear periphery. During meiosis the proteasome was found to undergo dramatic changes in its localization. Throughout the f irst meiotic division, the signal is more dispersed over the nucleus. Durin g meiosis II, there was a dramatic re-localization, and the signal became r estricted to the area between the separating DNA until the end of meiosis w hen the signal dispersed before returning to the nuclear periphery during s pore formation. These findings strongly imply that the nuclear periphery is a major site of protein degradation in fission yeast both in interphase an d throughout mitosis. Furthermore they raise interesting questions as to th e spatial organization of protein degradation during meiosis.