Can someone answer this ASAP? mRNA transcripts can contain multiple polyadenylat
ID: 69063 • Letter: C
Question
Can someone answer this ASAP? mRNA transcripts can contain multiple polyadenylation sites in their 3'UTR downstream of the STOP codon. The region between these polyA sites often contain regulatory sequences that can bind and interact with micro RNAs (miRNAs). Below is an example of such mRNA: In liver cells the mRNA above is polyadenylated at PA site 1, whereas in the brain it is polyadenlated at the PA site 2 and there is a miRNA-binding site in between these two PA sites. What can you tell me about the relative protein expression levels in the liver vs the brain for this particular transcript? How did you come to this conclusion? Explain in detail.Explanation / Answer
As miRNA-binding site is present before the PA2, it shows that mRNA synthesized in the brain is more likely to be degraded immediately after the synthesis by miRNA silencing mechanism. So, as a result of mRNA degradation, the protein synthesis of this gene is low in the brain, whereas the expression of the same is more in the liver.
RNA interference is initiated by DICER, which cleaves double small double stranded RNA known as miRNA. miRNA then binds to a heterodimer of R2D2 and Dcr-2 proteins. They form R2D2/Dcr-2 complex. The 5’end of the RNA interacts with Dcr-2 forming the pre-RISC complex. As the name indicates, the pre-RISC complex is the inactive form. TRBP is one of the integral components of the dicer-containing complex, and is required to recruit Ago2 protein. These proteins are important for interacting with the bound miRNA.
Ago2 protein activates the pre-RISC complex, and converts it into holo-RISC by binding the double stranded miRNA. After binding of Ago2, it degrades one of the strands of miRNA, and retaining the guide strand of miRNA. The holo-RISC complex with the help of guide strand recognizes the complementary mRNA. Once mRNA is bound, it is degraded by RISC complex.