| Summary: | 碩士 === 國立臺灣大學 === 分子與細胞生物學研究所 === 95 === Meiosis plays an important role in sexual reproduction. A diploid yeast cell undergoes meiosis and produces four haploid spores when nutrients are limited. The overall process of meiosis and spore formation is called sporulation.
Yeast small heat shock protein Hsp26 is considered as a chaperone cooperating with other heat shock proteins to prevent the aggregation of proteins under heat shock stress. Hsp26 is also induced during sporulation. Previous studies found that the sporulation efficiency of the hsp26 mutant is better than that of the wild type, and the cause seems to be at the stage of spore formation, not meiosis. To understand the molecular mechanism of Hsp26 action during sporulation, we studied two potential Hsp26-interacting proteins: Ady3 and Tem1. Ady3 is a component of the leading edge protein coat of the prospore membrane and is important for prospore formation and spore wall synthesis. Tem1 is a critical component in mitotic MEN pathway to terminate M phase and complete cytokinesis.
We found that more Ady3 signals were detected as the leading edge coat in the hasp26 mutant than in the wild-type control. This observation suggests that Hsp26 might be involved in the regulation of Ady3 localization onto the leading edge coat.
We were not able to confirm the interaction between Hsp26 and Tem1 by co-immunoprecipitation. However, we discovered an interesting pattern of Tem1 phosphorylation. Tem1 phosphorylation was detected after diauxic shift and maintained through sporulation. The phosphorylation could be caused by nutrient limitation, such as glucose inadequacy. Because TEM1 is an essential gene, we could not study the function of Tem1 in sporulation by a regular knock-out method. We used the conditional tem1-3 ts mutant to study Tem1 function in sporulation. Since the tem1-3 mutant displayed normal sporulation at restriction temperatures, Tem1 is probably not essential to sporulation. It was interesting that the tem1-3 mutant exhibited cytokinesis defects in early stationary phase even at permissive temperatures. Besides, we found that the tem1-3 mutant had impaired phosphorylation and displayed decreased viability in stationary phase. It indicates that Tem1 phosphorylation may be important for cell viability in stationary phase.
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