Question

Eukaryotic genes can be introduced into bacteria by recombinant DNA techniques. If the introduced gene encodes a protein that is also found in bacteria (for example, a universally used glycolysis enzyme) then, expression of the eukaryotic gene may produce a protein that functions in the bacterial cell. The mouse gene for a glycolysis enzyme is introduced into an E. coli cell that has a mutant gene for the bacterial version of the same enzyme. Even though the mouse enzyme should function in the bacterial cell and restore the cell's ability to perform glycolysis, it does not. Provide two possible reasons why this experiment does not work and propose a solution to overcome one of the problems you suggest.

Answer 1

Answer:

Introns are the non coding regions that are available in the eukaryotic genes, before being transcribed they get spliced out. Prokaryotic genes do not have introns and so the cells do not have intron splicing enzymes and hence cannot remove introns from the RNA. Hence if introns are present in the mouse gene, they will not be removed after it is transcribed in E.coli. If such RNA with introns is translated, it results in an altered protein with extra aminoacids or an incomplete protein.

1. The prokaryotic RNA polymerase does not recognize the eukaryotic promoter, so there is no transcription. A eukaryotic gene that will be introduced into bacteria for expression must be engineered to have a prokaryotic promoter.

2. There is no Shine–Dalgarno sequence in the eukaryotic gene promoter, so even if an mRNA is produced, the prokaryotic ribosome will not efficiently recognize the translational start site. If a prokaryotic promoter is used to express this gene, it should have the Shine–Dalgarno sequence within it.