The transcriptional activator protein LEF1 is expressed in developing hair folli
ID: 177607 • Letter: T
Question
The transcriptional activator protein LEF1 is expressed in developing hair follicles where it binds to specific DNA sequences (LEF1 binding sites) to regulate transcription of a gene which we will call “gene D”. The protein product of gene D, protein D, is responsible for dark colored hair. Mice lacking gene D encoding the “D” protein have defective hair formation and appear light-colored.
The figure below shows several DNA sequences to which LEF1 binds. The sequence on the top is the “optimal” LEF binding sequence. Sequences that best match the “optimal” sequence will be bound most strongly by LEF1. Of the two sequences depicted below the optimal sequence, which one represents the sequence found in blond Europeans (consider the information given about LEF1)?
Question 3 options:
Sequence 1
Sequence 2
impossible to say, not enough information
A)Sequence 1
B)Sequence 2
C)impossible to say, not enough information
G/CAT CA A A G optimal LEF1 binding sequence CA CTA A A G sequence 1 C GCT AAA G sequence 2Explanation / Answer
The correct answer is choice b, sequence 2.
Reason: It can be seen from the seqeunce of the reference DNA that the first three codons code for either histidien or asparagine amino acid. The next three code for glycine. In the sequence 1, the first amino acid encoded will be histidine and in the second sequence the first amino acid encoded will be arginine. Since the second codon is similar for both the mutated sequences, the position 1 of nucleotide is significant.
Thus, since sequence 2 changes identity of amino acid encoded, this seems to be the abundant binding site for LEF1 in the blonde populations.
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