1. How would eukaryotic translation initiation be affected if each of the follow

Question

1. How would eukaryotic translation initiation be affected if each of the following factors were nonfunctional? Would inactivating mutations in the genes that encode these factors be dominant or recessive? a) eIF2 b) eIF5

2. Histidine is encoded by two codons, 5’-CAU and 5’-CAC. However, yeast cells only make one type of histidine tRNA, which has a 3’-GUG anticodon. How are 5’-CAU codons translated?

3. a)What is the minimum length in nucleotides for the mRNA that encodes growth hormone?

b) Say you want to produce recombinant growth hormone for medical use. You place the human growth hormone gene into the bacteria E. coli. However, the E. coli don’t produce any growth hormone. List two reasons the human gene may not be expressed in E. coli

Explanation / Answer

1. Translation is the process in which the ribosomes in cell's cytoplasm create proteins, following transcription of DNA to mRNA in the cell's nucleus.

a. eIF2: It is a eukaryotic initiation factor. eIF2 mediates the binding of tRNAiMet to the ribosome in a GTP-dependent manner. eIF2 is a heterotrimer consisting of an alpha (also called sub-unit1), a beta (sub-unit 2), and a gamma (sub-unit 3) sub-unit. Once the initiation is completed, eIF2 is released from the ribosome bound to GDP as an inactive binary complex. To participate in another round of translation initiation, this GDP must be exchanged for GTP.

If eIF2 is non-functional, then the translation comes to a halt. eIF2 forms a ternery complex, and without this ternery complex no initiation step can occur. Also, low concentration of ternary complex allows the expression of GCN4(starved condition), which in turn, results in increased activation of amino acid synthesis genes.

b. eIF5: eIF5 functions in start site selection as a GTPase-accelerating protein(GAP) for the eIF2·GTP·tRNAiMet ternary complex within the ribosome-bound pre-initiation complex. Also, eIF5 is a critical component of the eIF2(alpha) regulatory complex that inhibits the activity of the guanine-nucleotide exchange factor (GEF) eIF2B.

So, if eIF5 becomes non-functional, the ternery complex formation will be halted as it regulates teh phosphorylation of eIF2. This would result in halting if the translation.

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