Ty Element Retrotransposition in Saccharomyces cerevisia

一年来，我们在以下方面取得了进展：通过将活性元件重新引入到因长末端重复（LTR-LTR）重组而失去常驻元件的无ty菌株中，研究了Ty1拷贝数的动态。重新繁殖的菌株表现出与Ty1插入相关的染色体大小改变，但不会成为遗传分离。在已知影响Ty1逆转录的遗传和环境条件下，已经使用遗传标记的参考元件确定了元件的增益和损失率。在不同条件下获得的Ty1增益和损失比表明，拷贝数随着时间的推移而变化，通过改变反转录转位的速率，导致在Saccharomyces中观察到不同的拷贝数。在更广泛的范围内，我们的研究结果表明，ltr -反转录转座子的获得和损失可能是高度动态的，并且有可能在短的进化时间内重塑基因组。在与Dwight V. Nissley博士（SAIC, Frederick MD）的合作中，我们已经证明了由Ty1和HIV-1逆转录酶基因组成的杂交元件是检测、监测和分离出芽酵母中耐药逆转录酶的有用工具。这种敏感的表型分析检测临床样品中的耐药变异，当变异仅占病毒种群的0.3%至1.0%时。此外，我们的检测方法可以检测已知的和新的逆转录酶变异，应该有助于研究轻微耐药变异的进化和临床意义。

Over the past year, we have made progress in the following areas. Ty1 copy number dynamics has been studied by reintroducing active elements into a Ty-less strain where resident elements had been lost by long terminal repeat (LTR-LTR) recombination. Repopulated strains exhibit alterations in chromosome size that are associated with Ty1 insertions, but do not become genetically isolated. The rates of element gain and loss under genetic and environmental conditions known to affect Ty1 retrotransposition have been determined using genetically tagged reference elements. Ty1 gain and loss ratios obtained under different conditions suggest that copy number oscillates over time by altering the rate of retrotransposition, resulting in the diverse copy numbers observed in Saccharomyces. On a broader scale, our results suggest that the gain and loss of LTR-retrotransposons can be highly dynamic and has the potential to remodel genomes over short evolutionary time periods. In collaboration with Dr. Dwight V. Nissley (SAIC, Frederick MD), we have shown that hybrid elements composed of Ty1 and the reverse transcriptase gene from HIV-1 are useful tools for detecting, monitoring, and isolating drug-resistant reverse transcriptases in budding yeast. This sensitive phenotypic assay detects drug-resistant variants in clinical samples when the variants comprise as little as 0.3 to 1.0% of the virus population. Furthermore, our assay can detect of both known and novel reverse transcriptase variants and should be useful in studies of the evolution and clinical significance of minor drug-resistant variants.