Question

The DNA sequence is repeated here:

5...Exon 1...AGCTTGGGAGCGGCG GTGAGGCGGGAGGCG...Intron 1...TCCTCTCTCCCCCAG GGCCCACCAGCTCTG...Exon 2...3
Recall that the DNA sequence that corresponds to intron 1 is underlined and bolded. You are now interested in using FISH to visualize the pattern of expression of this gene during mouse embryo development. This time you need to design a probe that will only bind the mature mRNA and not genomic DNA.
Note that often DNA probes are used to hybridize to RNA sequences. Which of the following DNA probes could you use to detect mature mRNA from this gene?

O 5' TCCTCTCTCC 3
O 3' GCCGCCCGGG 5'
O 3' GCCGCCACTC 5
O 3' AACCGTCGCC 5'
O 5' CGGCGGGCCC 3'
O 5CGGCGGTGAG 3

Answer 1

The correct FISH probe for detecting mature mRNA of this gene is 5' CGGCGGTGAG 3' because it matches the exon sequence and does not bind to any intronic sequences.

Step-by-step explanation:

To detect mature mRNA using fluorescence in situ hybridization (FISH), it is imperative to use a DNA probe that binds to the mRNA sequence excluding introns. Since mature mRNA will contain only the exons after RNA splicing, a probe matching the exonic sequence is necessary.

The given DNA sequence contains two exons flanking an intervening intron. Recognizing that introns are removed during the formation of mature mRNA, a suitable probe for FISH would only include sequences from the exons. Let's evaluate the options provided to find a probe complementary to the exon sequences:

• 5' TCCTCTCTCC 3' - This corresponds to a sequence found in the intron, hence, inappropriate.
• 3' GCCGCCCGGG 5' - This is a reverse complement of a sequence in exon 1, making it a contender.
• 3' GCCGCCACTC 5' - Incorrectly aligned with the exon-intron junction, not suitable.
• 3' AACCGTCGCC 5' - Incorrect, does not match any exon sequence.
• 5' CGGCGGGCCC 3' - Incorrect, matches the intron sequence.
• 5' CGGCGGTGAG 3' - Correct, matches the exon 1 sequence, suitable for detection.

The final answer is the probe 5' CGGCGGTGAG 3', as it corresponds to the sequence found only in mature mRNA and will not bind to any intronic sequences. The two line explanation is that introns are removed from mRNA during processing, therefore probes must be complementary to exon sequences.