Question

The human gene for a protein hormone has been isolated. Scientists want to introduce this gene into a bacterial host, modifying the bacteria so that it can be used to produce this hormone. After successfully introducing the gene on a plasmid, the bacteria produced the protein hormone, but the protein was defective, longer than normal, with intervening stretches of amino acids not found in the native protein. Which solution would be most likely to resolve this problem?

Multiple Choice

A. Treat the defective protein with enzymes.

B. Introduce human ribosomes into the bacteria.

C. Start over, introducing a complementary DNA (cDNA) copy of the gene into the bacterial host.

D. Introduce human mRNAs into the bacterial host.

Answer 1

The human gene is a eukaryotic gene. And a typical eukaryotic gene has exons and introns. Exons are the coding part of the gene and they code for the functional protein. The introns are removed from the primary transcript by the process of splicing.

The bacterial genes do not have introns and hence they do not possess the system to remove the introns. As a result, the protein that will be produced from the human gene in the bacteria will be longer and defective. It will also have amino acids coded for the intronic sequences.

To overcome this issue, an ideal strategy used is to isolate the processed mRNA from the human cells. This mRNA will be already processed and hence will lack the intronic fragments. Then this mRNA can be reverse transcribed in a test tube using reverse transcriptase and a PCR machine. The resultant fragment will be complementary DNA or cDNA sequence. When this cDNA is introduced into the bacteria, the problem of intronic fragments in the protein will be lost. And hence the desired protein hormone can be obtained from the bacterial system.

Therefore, the correct answer is C.