Question

You experimentally change the DNA sequence directly upstream of a start codon of an operon in E. coli to investigate the function of this region of DNA. Analysis reveals that after the change the same amount of mRNA is made from the operon, but there are very few proteins made from the operon. What is the most likely function of the DNA sequence that you changed
a. The DNA sequence likely functions as in transcriptional regulation.b. The DNA sequence likely functions as a termination sequence.c. The DNA sequence likely functions as a promoter.d. The DNA sequence likely functions as a ribosome-binding site.

Answer 1

Answer:

The correct answer is option d. "The DNA sequence likely functions as a ribosome-binding site".

Explanation:

The question states that a DNA region upstream of a start codon of an operon was changed to see its function. The result of the change was that the same amount of mRNA was made from the operon but very few proteins were expressed. This indicates that the DNA region that was changed most likely functions as a ribosome-binding site. This would explain why the translation level was affected but not the transcription level. A change in a ribosome-binding site would only affect the level of translation as a result of mRNA binding poorly to the ribosome.