Chiani Francesco, Di Felice Francesca, Camilloni Giorgio
Dipartimento di Genetica e Biologia Molecolare, Università di Roma La Sapienza, Rome, Italy.
Nucleic Acids Res. 2006;34(19):5426-37. doi: 10.1093/nar/gkl678. Epub 2006 Sep 29.
The null mutation of the SIR2 gene in Saccharomyces cerevisiae has been associated with a series of different phenotypes including loss of transcriptional silencing, genome instability and replicative aging. Thus, the SIR2 gene product is an important constituent of the yeast cell. SIR2 orthologues and paralogues have been discovered in organisms ranging from bacteria to man, underscoring the pivotal role of this protein. Here we report that a plasmid introduced into sir2Delta cells accumulates more negative supercoils compared to the same plasmid introduced into wild-type (WT) cells. This effect appears to be directly related to SIR2 expression as shown by the reduction of negative supercoiling when SIR2 is overexpressed, and does not depend on the number or positioning of nucleosomes on plasmids. Our results indicate that this new phenotype is due to the lack of Sir2p histone deacetylase activity in the sir2Delta strain, because only the H4-K16 residue of the histone octamer undergoes an alteration of its acetylation state. A model proposing interference with the replication machinery is discussed.
酿酒酵母中SIR2基因的无效突变与一系列不同表型相关，包括转录沉默丧失、基因组不稳定和复制性衰老。因此，SIR2基因产物是酵母细胞的重要组成部分。在从细菌到人类的各种生物体中都发现了SIR2直系同源物和旁系同源物，这突出了该蛋白质的关键作用。在此我们报告，与导入野生型（WT）细胞的相同质粒相比，导入sir2Δ细胞的质粒积累了更多的负超螺旋。如过表达SIR2时负超螺旋减少所示，这种效应似乎与SIR2表达直接相关，并且不依赖于质粒上核小体的数量或定位。我们的结果表明，这种新表型是由于sir2Δ菌株中缺乏Sir2p组蛋白脱乙酰酶活性，因为只有组蛋白八聚体的H4-K16残基的乙酰化状态发生了改变。文中讨论了一个提出干扰复制机制的模型。
