Conditions such as mad cow disease are caused by abnormally shaped proteins, called prions. Prions spread by causing other, normal proteins to misfold and adopt the abnormal shape—no genetic material like DNA is involved. Prion diseases affect the brains of a number of mammals, including humans. Although humans can get mad cow from beef, these unusual diseases rarely jump between species. Still, scientists say new forms of prion diseases have arisen lately, and there’s concern that they could hop to humans. So researchers want to understand the species barrier better. 

    A study published in the September 4th issue of the journal Cell investigates that issue. Scientists from Texas, Spain and Chile took normal hamster proteins and mixed them with misfolded mouse ones.  And the mouse prions were able to change the hamster proteins into a new kind of prion that infected both healthy hamsters and mice. The test tube is obviously an unnatural situation, but it shows that prions can leap the species barrier without the aid of any other infectious agent. Scientists hope to learn more about how this process works so they can keep prions in their place—away from humans.

    实验室研究表明：朊蛋白能越过物种壁垒

    疯牛病是由不正常形状的蛋白质引起的，这样的蛋白质叫做朊（音软）蛋白。朊蛋白传播的方式是通过使其它正常的蛋白质错误折叠从而改变正常的形状——这种蛋白质不具有像DNA一样的基因物质。朊蛋白病毒能影响很多哺乳动物的大脑，其中也包括人的大脑。虽然人可能从食用牛肉中感染疯牛病，但是这些怪异的疾病很少在不同物种之间传播。不过，科学家们说最近有新变种朊蛋白疾病出现，人们担心这些病毒可能会传染给人类。鉴于此研究者们想更好的认识病毒传播的物种壁垒。

    发表在9月4日《细胞》（Cell）杂志上的一项报告研究了这个问题。来自得克萨斯、西班牙以及智利的科学家们把正常的仓鼠蛋白和错误折叠的老鼠蛋白（即朊蛋白）混合在一起。老鼠朊蛋白能把仓鼠蛋白变为一种新的朊蛋白，这种新的朊蛋白能感染健康的仓鼠和老鼠。显然在试管里的情况是一种非自然状态，但是这项研究表明朊蛋白能在不借助于任何其它传染媒介的情况下跨越物种障碍。科学家们希望知道更多关于这些朊病毒传播过程的机理，从而控制这些病毒，使它们远离人类。

    Vocabulary:
    Prion:   朊蛋白；朊病毒；
    Misfold: 错误折叠
    Hop: 跳跃
    Barrier: 壁垒；障碍
    Hamster protein: 仓鼠蛋白
    Infect: 感染；形容词infectious