Tca2 is a Ty1/copia-type retrotransposon from the pathogenic yeast Candidaalbicans. It was originally identified as an abundant, linear, extrachromosomal, double-stranded DNA molecule. Here we show that Tca2 is widespread in C.albicans, but that the abundance of extrachromosomal Tca2 DNA varies greatly among different strains and is strongly dependent on the growth temperature. The relative levels of Tca2 RNA vary in a similar pattern to the extrachromosomal DNA, raising the possibility that the variations in extrachromosomal DNA levels are introduced predominantly at the level of transcription. We have also analysed the retrotranspositional activity of the element by developing a transposition assay involving a cloned Tca2 element tagged with a selectable marker gene that is activated by passage through an RNA intermediate. We show that the marked Tca2 is transpositionally active as transposed copies of the marked element became integrated at a variety of new positions in the genome and an intron in the donor element was precisely removed in the newly transposed copies. This is the first report of transposition in C.albicans.
Tca2 是致病酵母念珠菌中的 Ty1/copia 型转座子。它最初被鉴定为一种丰富的线性染色体外双链 DNA 分子。在这里,我们发现 Tca2 在白念珠菌中广泛存在,但不同菌株间染色体外 Tca2 DNA 的丰度差异很大,而且与生长温度密切相关。Tca2 RNA 的相对含量变化与染色体外 DNA 的变化相似,这就提出了一种可能性,即染色体外 DNA 含量的变化主要是在转录
水平上产生的。我们还通过开发一种转座试验分析了该元件的逆转座活性,该试验涉及一个克隆的 Tca2 元件,该元件上标记有可选择的标记
基因,通过 RNA 中间体激活该标记
基因。我们发现,标记的 Tca2 具有转座活性,因为标记元件的转座拷贝整合到了
基因组中的多个新位置,而且在新的转座拷贝中,供体元件中的一个内含子被精确地移除。这是关于白僵菌转座的首次报道。