Question

10. In watermelon the FR gene encodes resistance to fruit fly pests. FR+ plants are resistant and FR- plants are sensitive. mRNA for this gene is detectable in both the WT and the mutant. Sequencing of these alleles indicates that the mutant allele has a sequence altered so a splice site junction at the fifth intron/exon border is not recognized by the splicesome.

Draw a northern blot that would represent these facts. (Just the end result that shows how the mRNAs from WT and mutant are different.)

The WT protein is 259 amino acids in length. In the mutant, no FR protein is detected. Explain this observation.

Answer 1

The below diagram represents the Northern blot of the wild type and the mutant mRNA's Northern blot:

As the splice site in the mutant mRNA is changed and the intron is not cleaved, the mRNA of the mutant will be having more nucleotides than the wild type mRNA. This can be seen in the northern blot above.

The wildtype mRNA is able to proceed to produce a 259aa length protein, but the mutant is not able to produce this protein. This maybe due to the presence of the intron sequence which might be having a stop codon in it and hence the incompletely translated protein might undergo ubiquitination as it will be seen as a foreign protein by the cell.

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