Hi, I need help interpreting this experiment.
The locations of the TATA box in two species of yeast, Schisosaccharomyces
pombe and Saccharomyces cerevisiae differ dramatically. The TATA box of S.
pombe is about 30 nucleotides upstream of the start site, similar to the location in most other eukaryotic cells. However, the TATA box of S. cerevisiae is 40 to 120 nucleotides upstream of the start site. To better understand what establishes the transcriptional start site in these two
species, researchers conducted a series of experiments to determine which
components of the transcription apparatus of these two species could be
interchanged. In these experiments, different transcription factors and RNA
polymerases were combined, and the effects of the switch on the level of RNA synthesis and on the start point of transcription were observed. The results from one set of experiments are shown in the table. Components preceded with a “c” are factors from S. cerevisiae. Components preceded with a “p” are factors from S. pombe. The table indicates whether the components were present (+) or absent (-) in the experiment. In the gel, the presence of a band indicates that RNA was produced and the position of the band indicates whether it was the length predicted when transcription begins 30 bp downstream from the TATA box or from 40 to 120 bp downstream from the TATA box. The gel has larger molecules at the top, and shorter molecules toward the bottom. The table aligns with the gel, and indicates what is present in each reaction.
Experiment (gel lane #)
Components 1 2 3 4 5 6 7
cTFIIE + - + + + + -
cTFIIH + cTFIIF + - + + + - +
cTFIIB + cPol II + - - - - - -
pPol II - + + + - + +
pTFIIB - + + - + + +
pTFIIE + pTFIIH + pTFIIF - + - - - - -
Gel electrophoresis bands
30 bp TATTA box. = =
40 to 120 bp =
TATTA box
The question asks about conclusion regarding the components determine the start site for transcription? I am confused on how some of these transcription components or polymerases working and not working in the some trials. I think the 40 to 120 bp segment is smaller thus farther down compared to the 30 bp segment.
Thanks!