Discussion
The effect of mutations in a gene at their transcriptional and translational levels were analyzed using Northern (N) and Western (W) blot techniques, respectively. The following figure shows the schematic representation of mRNA and protein expression profiles of the wild-type and its four different mutants. Which one of the following mutants contains mutation in the upstream regulatory region of the gene?
Answer: D
The mutation in the upstream regulatory region is in Mutant-4.
Mutant-4 shows no band on either blot: no mRNA on the Northern blot and therefore no protein on the Western blot. Transcription itself has failed, which is what happens when the promoter or another upstream regulatory element is destroyed.
Mutants 1, 2 and 3 all make mRNA of normal size, so their transcription is intact. Their proteins differ in size: smaller in Mutants 1 and 2 (the band runs lower), as from a premature stop codon in the coding region, and larger in Mutant 3, as when a stop codon is lost. Those are mutations in the coding sequence, not in the regulatory region.
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