问题 问答题

TFA是5s rRNA基因表达所需的转录因子,这个蛋白含有9个锌指结构域,与5s rRNA基因内的一段序列和5s rRNA本身结合。(1)如何定位TFⅢA蛋白的DNA结合位点(2)什么样的突变可以证明锌指是DNA结合所需的(3)有人发现TFⅢAC端缺失19个氨基酸后与DNA结合的能力与野生型一样,但是不能激活5S rRNA基因的转录,请解释原因。(4)非洲爪蟾(Xeropus laevis)的卵母细胞中合成并贮存了大量的5S rRNA,随着5S rRNA的积累,TFⅢA与之结合,这对5S rRNA基因的转录有何影响调控这个过程的机制是什么

答案

参考答案:(1)利用足迹法或碱基修饰法定位TFⅢA蛋白的DNA结合位点。(2)影响到锌指结构形成的突变(如无法形成TFⅢA蛋白C端α-螺旋的突变),可证明锌指是DNA结合所需的。(3)TFⅢAC端的非保守性氨基酸可能负责识别特异的DNA目标位点,C端缺失19个氨基酸后,虽与DNA结合的能力不变,但由于DNA特异位点的选择出现问题,所以无法激活5s rRNA基因的转录。(4)随着5srRNA的积累,TFⅢA与之结合,这对5s rRNA基因的转录具有阻抑作用。调控这个过程的机制是自体调控。

阅读理解

阅读理解。

Dear Lucy,

      How are you? Now,  I'm going to tell you something.  Last week we had a journey to Mount Tai. 

 On Tuesday we flew to Tai' an,a city at the foot of the mountain.  We had a good rest at a hotel.  At

about three o'clock early next morning, we began to climb the mountain. It look us about two hours

and a half to reach the top. The mountain is covered with forest.  I've never seen such a beautiful place.

     "Look! The sun is going to rise!" someone shouted.

     We all turned to the east and watched.  Soon half of the sky became white, and a big, red ball was

going up slowly from the sky.  A few minutes later, all the world was bright.

     We stayed on the top and had a good time.  After lunch we started going down.  We got to our hotel

at about four in the afternoon. Though we were tired, we were very happy.  We came back to school the

next day.

     Thank you very much for your last letter and the wonderful stamps.  Hope to hear

from you soon.

                                                                                                                Yours,

                                                                                                               Wu Dong

根据信件内容,判断正(T)误(F)。

(     )1.  The letter is from Wu Dong to Lucy.

(     )2.  There are many trees all over Mount Tai.

(     )3.  Wu Dong watched the sun rising at the top of the mountain.

( )4.  Lucy had sent some stamps to Wu Dong before he wrote the letter.

(     )5.  The letter doesn't tell us when Wu Dong returned to the hotel.

单项选择题 A1/A2型题