8. The locations of the TATA box in the genes of two species of yeast, Saccharom

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8. The locations of the TATA box in the genes of two species of yeast, Saccharomyces pombe and S. cerevisioe, differ dramatically. The TATA box of S. pombe is about 30 nucleotides upstream of the start site, similar to the location for most other eukaryotic cells. However, the TATA box of S. cerevisioe is 40 to 120 nucleotides upstream of the start site. ! To better understand what sets the Components start site in these organisms researchers at Stanford University conducted a series of experiments to eTFIB + cPol II determine which components of thepPol II transcription apparatus of these two eTFIIE pTFIB species could be interchanged (Y. U IIIFHF et al. 1994. Science 263:805-807). In these experiments, different general transcription factors and RNA polymerases were switched in S. pombe and S. cerevisiae, and the effects of the switch on the level of RNA synthesis and on the start point of transcription were observed in a series of tests. The results from one set of experiments are shown in the table. Components cTFIIB, cTFIIE, cTFIIF, and cTFIIH are transcription factors from S. cerevisioe. Components pTFIIB, pTFIIE, pTFIF, and pTFIlH are transcription factors from s. pombe. Components cPol Il and pPol Il are RNA polymerase II from S cerevisioe and S. pombe, respectively. The table indicates whether the component was present () or missing (-) in each of the tests (1-7). In the accompanying gel, the presence of a band indicates that RNA was produced and the position of the band indicates whether it was the length predicated when transcription begins 30 bp downstream from the TATA box or from 40 to 120 bp downstream from the TATA box. Transcription at S. pompe start site (30 bp downstream from TATA box) Transcription at S. cerevisisae start site (40-120 bp downstream from TATA box) Gel A. What is a general transcription factor? (0.5 pt) B. What components appear to be necessary for transcription to occur in the experiment? Explain. (0.5 pt) necessary for recognition of the S pompe start site? Explain t0.S pt)

Explanation / Answer

a) General transcription factors or basal transcription factors are proteins that bind to promoter regions of the DNA to activate transcription.

b) TFIIE, TFIIB and the corresponding RNA polymerase II.

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