loading15．比较DNA结合蛋白和RNA结合蛋白的结构差异。
16．DNA双螺旋的哪些特征在决定DNA和结合蛋白相互作用的性质方面起着重要作用？ 17．描述DNA核结合蛋白相互接触的类型。为什么许多DNA结合蛋白呈二聚体形式？ 18.什么是激活蛋白？激活蛋白如何影响RNA聚合酶II起始复合物的装备？ 19．何为第二信使？请列出两种第二信使介导的信号转导的例子。
20．描述基因组重排是如何加强酿酒酵母中的交配型转变过程，脊椎动物免疫球蛋白多样性的产生过程。
21.Compare the mechanisms used by zinc-binding, leucine zipper, and HLH motifs to bind DNA. What is the role of zinc in the zinc-binding domain?
22.Describe the physical characteristics of a typical transcriptional activation region. How are these characteristics thought to reflect the mechanism of activation? If a novel transcription factor is identified, and you would like to locate the domain within the protein that is responsible for activation, how would you do this?
23.To determine how an activator contributes to the formation of the holoenzyme at your favorite promoter, design an experimental strategy to tell you which components are directly recruited by the activator, and which of these activator-mediated recruitment steps are required for transcriptional activation. How could you test whether the role of the activator stops with the holoenzyme assembly, or if it also induces allosteric changes within the DNA or the holoenzyme?
24.You transform a population of cells with a transgene, and isolate a cell line that has integrated the gene into its genome, but in which the gene is not expressed. Speculate as to what may be preventing the gene from being expressed. Describe two ways to test this possibility.
25.You isolate a mutant strain of mice that grow at an unusually fast rate, perform a blood test on the mice, and find that they have elevated levels of insulin-like growth factor. The phenotype is the result of a mutation in a region of the genome containing a gene encoding a DNA methylase. What kind of mutation is causing the rapid growth of these mice?
26.Eukaryotic signal transduction pathways often involve multiple proteins transmitting a signal from the cell surface to the nucleus. What advantage is gained through the use of multiple steps? Many signal transduction pathways are used in different cell types for entirely different purposes, leading to the transcription of different genes. How might different cell types be able to use a single signal transduction pathway to bring about such different results?
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27.Describe how yeast ensures proper expression of cell-type specific genes in a/ diploid cells, and in a or haploid cells. What phenotype would result from mutations in the following genes: a1, 1, 2, and mcm1?
25.What is the role of insulators in the regulation of transcription? Design a screen that could be performed to isolate novel insulators.
28.List three examples of gene repression in eukaryotes and describe the mechanism used by each of the repressors to prohibit transcription. How do these compare to mechanisms of prokaryotic repression? 29.Describe the role of acetylation and methylation of nucleosomes in silencing in the yeast S. pombe. What effect do these modifications have on chromatin structure and on gene expression?
30.Describe an example of a mechanism that results in a transient change in transcription of a gene, and one that produces a change that is maintained through cell generations, even in the absence of the initiating signal.
31.Describe regulation of the heat shock HSP70 promoter. What is the advantage of such a mechanism for response to heat or other stresses?
32.Drosophila sex determination is controlled by the activity of the Sxl protein. How does the cell initially achieve activity of Sxl exclusively in female cells, and how is this activity maintained? How does Sxl promote female identity in cells, and the absence of Sxl promote male identity?
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