Lesage P, Todeschini A L
Institut de Biologie Physico-Chimique, CNRS UPR 9073, Paris, France.
Cytogenet Genome Res. 2005;110(1-4):70-90. doi: 10.1159/000084940.
The aim of this review is to describe the level of intimacy between Ty retrotransposons (Ty1-Ty5) and their host the yeast Saccharomyces cerevisiae. The effects of Ty location in the genome and of host proteins on the expression and mobility of Ty elements are highlighted. After a brief overview of Ty diversity and evolution, we describe the factors that dictate Ty target-site preference and the impact of targeting on Ty and adjacent gene expression. Studies on Ty3 and Ty5 have been especially informative in unraveling the role of host factors (Pol III machinery and silencing proteins, respectively) and integrase in controlling the specificity of integration. In contrast, not much is known regarding Ty1, Ty2 and Ty4, except that their insertion depends on the transcriptional competence of the adjacent Pol III gene and might be influenced by some chromatin components. This review also brings together recent findings on the regulation of Ty1 retrotransposition. A large number of host proteins (over 30) involved in a wide range of cellular processes controls either directly or indirectly Ty1 mobility, primarily at post-transcriptional steps. We focus on several genes for which more detailed analyses have permitted the elaboration of regulatory models. In addition, this review describes new data revealing that repression of Ty1 mobility also involves two forms of copy number control that act at both the trancriptional and post-transcriptional levels. Since S. cerevisiae lacks the conserved pathways for copy number control via transcriptional and post-transcriptional gene silencing found in other eukaryotes, Ty1 copy number control must be via another mechanism whose features are outlined. Ty1 response to stress also implicates activation at both transcriptional and postranscriptional steps of Ty1. Finally, we provide several insights in the role of Ty elements in chromosome evolution and yeast adaptation and discuss the factors that might limit Ty ectopic recombination.
本综述的目的是描述Ty逆转录转座子（Ty1 - Ty5）与其宿主酿酒酵母之间的亲密程度。重点介绍了Ty在基因组中的位置以及宿主蛋白对Ty元件表达和移动性的影响。在简要概述Ty的多样性和进化之后，我们描述了决定Ty靶位点偏好的因素以及靶向作用对Ty和相邻基因表达的影响。关于Ty3和Ty5的研究在揭示宿主因子（分别为Pol III机制和沉默蛋白）和整合酶在控制整合特异性中的作用方面尤其具有启发性。相比之下，对于Ty1、Ty2和Ty4，除了它们的插入取决于相邻Pol III基因的转录能力并且可能受某些染色质成分影响外，人们了解得并不多。本综述还汇总了关于Ty1逆转录转座调控的最新发现。大量参与广泛细胞过程的宿主蛋白（超过30种）直接或间接控制Ty1的移动性，主要是在转录后步骤。我们重点关注了几个基因，对它们进行更详细的分析有助于构建调控模型。此外，本综述描述了新的数据，这些数据表明对Ty1移动性的抑制还涉及两种在转录和转录后水平起作用的拷贝数控制形式。由于酿酒酵母缺乏其他真核生物中通过转录和转录后基因沉默进行拷贝数控制的保守途径，Ty1的拷贝数控制必须通过另一种机制，其特征在此进行了概述。Ty1对压力的反应也涉及Ty1在转录和转录后步骤的激活。最后，我们对Ty元件在染色体进化和酵母适应性中的作用提供了一些见解，并讨论了可能限制Ty异位重组的因素。
