Question

I. You found that protein expression in Lungs results in the production of a longer version of an mRNA that normally has two exons. You also know that E protein does not affect poly-A addition. When you look at the protein product of this lung mRNA you find that it is smaller than the normal protein. What step does E protein affect in Lungs and explain how the shorter protein might be produced?

II. You find that E protein expression in Kidneys results in the production of a shorter 3- domain version of a 4-domain protein and you notice that it is always the same domain that is missing. Explain what step does E protein affect in Kidneys?

III. You find that E protein expression in Liver results in the production of altered mRNAs that lack a poly-A tail. What step does E protein affect in the Liver?

Answer 1

Solution:

1. The shorter mRNA produced might be due to the inhibition to splicing of the exon 1 with exon 2. This inhibition results in the production of shorter mRNA than normal that inturn produces small truncated non-functional protein.

2. The E protein like in lungs, inhibits the splicing of exons. This E protein act as splicing inhibitor which inhibits the splicing of some exond, and results in the production of small proteins.

3. In liver the E protein is found inhibiting one of the important post transcriptional modification called a addition of poly A tail to the 31 end of the mRNA. This protein might be inhibiting the capacity of poly A polymerase to add poly adenine to the 31 end. This mRNA would be destabilized and attacked by exonucleases.