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.

    實(shí)驗(yàn)室研究表明：朊蛋白能越過(guò)物種壁壘

    瘋牛病是由不正常形狀的蛋白質(zhì)引起的，這樣的蛋白質(zhì)叫做朊（音軟）蛋白。朊蛋白傳播的方式是通過(guò)使其它正常的蛋白質(zhì)錯(cuò)誤折疊從而改變正常的形狀——這種蛋白質(zhì)不具有像DNA一樣的基因物質(zhì)。朊蛋白病毒能影響很多哺乳動(dòng)物的大腦，其中也包括人的大腦。雖然人可能從食用牛肉中感染瘋牛病，但是這些怪異的疾病很少在不同物種之間傳播。不過(guò)，科學(xué)家們說(shuō)最近有新變種朊蛋白疾病出現(xiàn)，人們擔(dān)心這些病毒可能會(huì)傳染給人類。鑒于此研究者們想更好的認(rèn)識(shí)病毒傳播的物種壁壘。

    發(fā)表在9月4日《細(xì)胞》（Cell）雜志上的一項(xiàng)報(bào)告研究了這個(gè)問(wèn)題。來(lái)自得克薩斯、西班牙以及智利的科學(xué)家們把正常的倉(cāng)鼠蛋白和錯(cuò)誤折疊的老鼠蛋白（即朊蛋白）混合在一起。老鼠朊蛋白能把倉(cāng)鼠蛋白變?yōu)橐环N新的朊蛋白，這種新的朊蛋白能感染健康的倉(cāng)鼠和老鼠。顯然在試管里的情況是一種非自然狀態(tài)，但是這項(xiàng)研究表明朊蛋白能在不借助于任何其它傳染媒介的情況下跨越物種障礙。科學(xué)家們希望知道更多關(guān)于這些朊病毒傳播過(guò)程的機(jī)理，從而控制這些病毒，使它們遠(yuǎn)離人類。

    Vocabulary:
    Prion:   朊蛋白；朊病毒；
    Misfold: 錯(cuò)誤折疊
    Hop: 跳躍
    Barrier: 壁壘；障礙
    Hamster protein: 倉(cāng)鼠蛋白
    Infect: 感染；形容詞infectious