Smilin is a (hypothetical) protein that causes people to be happy. It is inactive in many chronically unhappy people. The mRNA isolated from a number of different unhappy persons in the same family was found to lack an internal stretch of 173-nucleotides that are present in the Smilin mRNA isolated from a control group of generally happy people. The DNA sequences of the Smilin genes from the happy and unhappy persons were determined and compared. They differed by just one nucleotide change—and no nucleotides were deleted. Moreover, the change was found in an intron.
Can you hypothesize a molecular mechanism by which a single nucleotide change in a gene could cause the observed internal deletion in the mRNA? Be sure to include a comparison of the mechanism that is involved between what happens in the normal and mutant transcript.
What consequences for the Smilin protein would result from removing a 173-nucleotide-long internal stretch from the coding region of the Smiling mRNA?