分子生物学Chapter4.ppt

Review Eukaryotic RNA polymerase: The helix-loop-helix should not be confused with the helix-turn-helix. HLH is one of the DNA-binding motifs found in eukaryotes. And HTH is the main DNA-binding motif of prokaryotes. 注意不要将螺旋-环-螺旋结构与螺旋-转角-螺旋相混淆。 HLH基序是真核生物DNA结合基序中的一种，而HTH基序是原核生物中的主要DNA结合基序。 Let’s have a look at the 3D structure of mouse HLH. 我们来看一看小鼠HLH基序的3D结构。 OK, the last section we are going to discuss is about the experiments made to find out the RNA polymerase targets and the modularity of Specific Transcription Factors. 呃，我们要讨论的最后一节关于两项实验研究方面的内容。一是关于RNA聚合酶的目标，二是关于特异转录因子的模块化。 First, about RNA polymerase targets. We have already learned that eukaryotes have three different RNA polymerases. We also learned that RNA polymerase I mainly produces rRNA. RNA polymerase II mainly produces mRNA and RNA polymerase III mainly produces tRNA. But, how did we know? 首先，关于RNA聚合酶的目标。我们已经知道，真核生物拥有三种不同的RNA聚合酶，其中RNA聚合酶I主要产生rRNA，RNA聚合酶II主要产生mRNA，RNA聚合酶III主要产生tRNA。但是，一开始是怎么知道的呢？ Why is alpha-amanitin so poisonous to human beings? Studies indicated that alpha-amanitin inhibits the three eukaryotic RNA polymerases to very different extents. Low concentrations completely inhibit RNA polymerase II, but have no effect on the activity of the polymerases I and III. Much higher concentrations can also inhibit RNA polymerase III, but still have no effect on RNA polymerase I. 为什么α鹅膏蕈碱对人类有这么大的毒性？研究发现，该毒素对三种不同的真核RNA聚合酶的抑制程度有很大差别。低浓度的毒素完成抑制RNA聚合酶II，而对其它聚合酶的活性没有任何影响。更高浓度的毒素也能抑制RNA聚合酶III，但仍然对RNA聚合酶I没有影响。 In order to see which genes are transcribed by which polymerase, cells are exposed to α-amanitin. It was found that, under very high concentrations of α-amanitin, only rRNA precursor is produced. This means that rRNA precursor is produced by RNA polymerase I. 为了弄清哪些基因由哪种聚合酶转录，细胞被暴露在α鹅膏蕈碱中。暴露在很高浓度α鹅膏蕈碱的细胞只产生rRNA前体，意味着这正是RNA聚合酶I所转录的基因。 Then, cells expose to low concentrations of the toxin also produce tRNA and other small RNAs like the 5S rRNA, suggesting that these are the genes tran