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?
Mutation occurred in ribosome binding site that serves as binding site for 30S ribosomal subunit of <em>E. coli</em> and allows the process of protein synthesis to begin.
Explanation:
The initiation of protein synthesis in bacteria requires binding of the ribosome to the ribosome binding site. The ribosome binding site in bacteria consists of the initiation codon "AUG" and the preceding Shine-Dalgarno sequence. The AUG initiation codon and Shine Delgrano sequence are around 10 bases apart.
The sequence is polypurine hexamer and is represented by 5' ...AGGAGG...3'. Shine-Delgrano sequence is complementary to the conserved sequence present at the 3' end of 16SrRNA of the 30S subunit of the bacterial ribosome. Binding of Shine Delgrano sequence of ribosome binding site and the complementary sequence of the 30S ribosomal subunit marks the first step in the initiation of protein synthesis.
Any mutation in the ribosome binding site would not allow the process of protein synthesis to start or would reduce the rate of the initiation of protein synthesis.
The answer is (A) stabilizing selection. Stabilizing selection favors the average in a population. In this case, babies that are born at a normal body weight, or an average between the two extremes of underweight and large, tend to have more favorable outcomes.
