Question

During initiation of translation in eukaryotes the start codon must be correctly positioned in the P-site in order to successfully start translation. One of the primary ways that this can occur is that the ribosome binds to the 5' cap and then scans along the mRNA until it encounters a start codon where the final ribosome, tRNA, mRNA complex can form. In some mRNA's, sequences in the 5' UTR can regulate translation by modulating the ability of the ribosome to perfom this scan. In other words 5' UTR sequences participate in turning on and turning off translation. Based on what you know about the 5' UTR as well as RNA in general and other similar biological mechanisms that you have learned about in other contexts in this class, propose a reasonable way that the 5' UTR could be involved in translation regulation.  

Answer 1

An mRNA transcript consists of untranslated flanking regions (UTRs) on both 5' and 3' ends. It is proposed that the 5' UTR can regulate the process of translation by many ways- by forming secondary structure, by preventing the pre-initiation complex formation, by ferritin regulation, by closed loop formation etc..

5' UTR mediated translation regulation by forming closed loop with 3' UTR- During eukaryotic translation initiation, a translation initiation factor known as eIF4E directs the ribosomes to the cap structure of the mRNA and binds to the 5' UTR. In some instances, this eIF4E - 5'UTR complex binds to the CPEB protein (Cytoplasmic Polyadenylation Element Binding Protein) present at the 3' UTR. This interaction between the 5' and 3' UTRs makes the mRNA transcript structure a closed loop. As a result of this loop formation the mRNA becomes translationally inactive. This is one way 5' UTR regulates eukaryotic translation.