Brodeur G M, Sandmeyer S B, Olson M V
Proc Natl Acad Sci U S A. 1983 Jun;80(11):3292-6. doi: 10.1073/pnas.80.11.3292.
Sigma is a recently described family of transposable elements in yeast (Saccharomyces cerevisiae). The most striking feature of the seven sigma elements that have been previously identified is that all are located 16-18 base pairs upstream from tRNA-encoding regions. Because these cases were all encountered in the process of studying specific tRNA genes, the full extent of the association between sigma elements and tRNA genes could not be assessed. In this paper, we report a more global characterization of the sigma family in a typical laboratory yeast strain: of the 30 copies of sigma that we estimate to be present in the haploid genome, we have cloned and analyzed 25 loci. Although in two cases a pair of sigma elements were found within several kilobases of each other, the majority occur as individual elements at widely dispersed sites. Moreover, in all 25 cases analyzed, the sigma elements are closely associated with tRNA genes. Thus, the sigma transposable element has been shown to have an absolute association with another gene family.
西格玛（Sigma）是最近在酵母（酿酒酵母）中发现的一个转座子家族。先前已鉴定出的七个西格玛元件最显著的特征是，它们都位于编码tRNA区域上游16 - 18个碱基对处。由于这些情况都是在研究特定tRNA基因的过程中遇到的，所以无法评估西格玛元件与tRNA基因之间关联的全貌。在本文中，我们报告了在一个典型实验室酵母菌株中西格玛家族更全面的特征：我们估计单倍体基因组中存在30个西格玛拷贝，已克隆并分析了其中25个位点。尽管在两个案例中发现一对西格玛元件彼此相距几千碱基，但大多数是以单个元件的形式出现在广泛分散的位点。此外，在所有分析的25个案例中，西格玛元件都与tRNA基因紧密相关。因此，已证明西格玛转座子与另一个基因家族存在绝对关联。
