新的基因编辑技术诞生，更精准，风险更小

Scientists in the US have developed a powerful new genome editing system that could offer significantly more precision and efficiency than the current CRISPR standard.
美国科学家已研发出强大的新的基因组编辑系统，显著提高目前CRISPR标准的精度和效率。
While CRISPR-Cas9 is a revolutionary medical technology that lay the modern foundations for editing genetic code – including variants associated with disease – there have long been concerns over its potential for imprecision.
虽然CRISPR-Cas9是革命性的医疗技术，为编辑包括与疾病相关的变异在内的遗传密码奠定了现代基础，但一直存在对其潜在的不精确性的担忧。
Specifically, many fear that CRISPR-Cas9 editing carries the potential to introduce errors in the form of uncontrolled insertions and deletions in genetic code, called indels.
具体来说就是很多人害怕CRISPR-Cas9编辑有可能在被称为索引的遗传密码中不受控制的插入和删除信息从而导致错误。

Researchers say the new system, dubbed 'prime editing' by its inventors at the Broad Institute of MIT and Harvard University, could change the game thanks to a new protein that enables high-precision edits of genetic targets.
研究人员说被麻省理工学院和哈佛大学的布罗德研究所的发明者称为“先导编辑”的这一新系统能改变基因，有一种新型蛋白质使研究人员可以对目标基因进行高精度编辑。
"A major aspiration in the molecular life sciences is the ability to precisely make any change to the genome in any location," says genome biologist David Liu from the the Broad Institute.
布罗德研究所的基因组生物学家David Liu说：“分子生命科学的一个主要目标是能精确改变任何位置的基因组。”
"We're not aware of another editing technology in mammalian cells that offers this level of versatility and precision with so few byproducts."
“我们不知道有其他对哺乳动物细胞进行编辑的技术能像这一技术一样用途广泛、精度高，而且副作用这么少。”
The basis of the new prime editing method is an enzyme called reverse transcriptase. The CRISPR system also uses an enzyme – Cas9 – to cut DNA strands, so that alternative genetic code can be inserted.
这一新的先导编辑方法的基础是被称为逆转录酶的酶，CRISPR系统也利用这种Cas9酶切割DNA链，插入替代遗传密码。
Now, thanks to reverse transcriptase, which is used in conjunction with Cas9 in prime editing, genomic editing has been upgraded again.
现在多亏有了逆转录酶，基因组编辑再次升级了。逆转录酶与Cas9一起被用于先导编辑。
In prime editing, a guide RNA called pegRNA guides a modified form of the Cas9 enzyme to snip only a single strand of DNA (preventing the double-strand breaks that can induce unintended disruptions).
先导编辑中名为pegRNA的引导RNA指引修改过的Cas9酶只剪断一条DNA链（避免双链断裂导致意外中断）。
After this, the reverse transcriptase enzyme directly copies edited genetic information contained in the pegRNA to the targeted genomic site.
然后逆转录酶直接将pegRNA中编辑过的基因信息复制到基因组的目标位置。