Question

1. Using Western Blot analysis, you have determined that protein levels of the insulin receptor increase in cultured fibroblast cells after treatment with a new drug. Which of the following hypotheses could explain how this drug could increase protein levels (select all correct answers).

   A	The drug could increase export of the mRNA from the nucleus, thus increasing mRNA levels and protein levels.
   B	The drug could increase expression of the gene, therefore increasing mRNA levels and protein synthesis.
   C	The drug could decrease the rate of protein degradation, inhibiting ubiquitination of the protein so more protein remains in the cell.
   D	The drug could shorten the polyA tail on the mRNA, therefore increasing the time the mRNA is available.
   E	The drug could influence the rate of protein synthesis, creating more protein in a given amount of time.

Answer 1

In eukaryotes, regulation of gene expression can be done at multiple levels - genomic, transcriptional, post-transcriptional, translational, post-translational levels.

Options A, C and E should be correct according to my opinion.

Option A selective export of mature mRNA can result in increase protein synthesis due to faster availability of mRNA in cytoplasm for translation.

Option B is very vague statement. Gene expression refers to transcription (mRNA synthesis) and translation (protein synthesis). So it is an unclear statement.

Option C can increase the protein levels. Ubiquitinization is a process by which multile ubiquitin tags are attached to a cellular protein, which is then digested or degraded by proteasome system. Inhibiting ubiqutinization may result in increased protein levels.

Option D cannot result in increase in protein levels; as shortening the polyA tail is actually a sign of an mRNA with a low half life i.e. it is degraded faster. So shortening the polyA tail will decrease the protein level rather than increasing.

Option E can result in increase in protein levels if it results in rate of protein synthesis which could be done by increase in initiation of translation or by positively influencing other steps.