Chromosome stability and cellular senescence in yeast aging gene project

1 .酵母HTR1基因的衰老机制HTR1和SGS1两个基因的产物被认为参与了酵母细胞的衰老过程。我们构建了一个双突变体，发现两个基因是上位性的。HTR1p与GFP的融合产物定位于细胞质中。HTR1基因的缺失导致了羟基脲的超敏感性，这种敏感表型被HTR1突变体的一个多拷贝抑制因子所挽救。由于这种抑制基因产物被证明是一种辅助抑制因子，特别是与SIR复合物相关的异染色质区域的基因，因此衰老信号必须从HTR1传递到SIR，最后传递到异染色质中的基因。2: SGS1基因的功能另一个老化基因SGS1的产物被证明与DNA拓扑异构酶相互作用。为了观察染色体结构的改变和细胞衰老的程度，我们用绿色荧光蛋白标记了DNA拓扑异构酶的不同片段。在这些融合产物中，有些与核仁亲和力较强，而与染色体亲和力较弱。这一观察结果的遗传学意义尚未被研究，但我们得到了非常有趣的线索，了解核仁在衰老过程中的功能与DNA拓扑异构酶的关系。

1 : Aging mechanism by yeast HTR1 geneThe products of two genes, HTR1 and SGS1 are suggested to involve in the cellular aging process in yeast. We constructed a double mutant and found that two genes were epistatic. The fusion product of HTR1p with GFP was localized in the cytoplasm. The deletion of HTR1 gene conferred the ultra sensitivity to hydroxyurea, and this sensitive phenotype was rescued by one of the multi copy suppressor of htr1 mutant. Since this suppressor gene product was shown as a corepressor particularly for the genes in heterochromatin region associated with SIR complex, the senescence signal must be transmitted from HTR1 to SIR and finally to the genes in heterochromatin.2 : Function of SGS1 geneThe product of another aging gene SGS1 was shown to interact with DNA topoisomerases. To visualize the alteration of chromosome structure and the extent to cellular senescence, we marked various fragments of DNA topoisomerases with GFP. Among these fusion product, some showed strong affinity to nucleolus, rather than to chromosomes. The genetical meaning of this observation is yet to be investigated, but we got very interesting clue to understand nucleolus function in aging process in relation to DNA topoisomerases.