Question

Predict the most likely observed level of luciferase activity if plasmid pCDγ3-789 is introduced into nonlymphoid cells such as a line of kidney tissue cells. Provide reasoning to justify your prediction.

Answer 1

Full information in question:

CD3 is a signaling protein that is typically found only in the plasma membrane of immune system T lymphocytes. CD3 is composed of several different polypeptides, including a gamma chain, CD3γ . Scientists analyzed the promoter of the CD3γ chain gene for regulatory sequences that might have positive or negative effects on expression of the gene. The scientists cloned fragments of the CD3γ gene that included the first transcribed nucleotides plus up to 789 nucleotides of upstream regulatory sequences into plasmids in which the gene for the firefly enzyme luciferase immediately follows the fragments. The plasmids were then introduced into a line of T lymphocytes (Figure 1), and the cells were allowed to grow for a short while. Because the regulatory sequences of the CD3γ gene immediately precede the luciferase gene in the plasmids, the activity, either positive or negative, of the regulatory sequences affected the amount of luciferase gene expression by the T lymphocytes. Luciferase catalyzes a reaction that results in the release of light and is responsible for the bioluminescence (light flashes) of fireflies. By quantifying the bioluminescence, or luciferase activity, in the cells, the scientists were able to determine the effects of each CD3γ gene fragment cloned into the plasmids (Figure 2) on expression of the gene.

Answer:

Luciferase activity will be absent

Explanation:

The regulatory element introduced into the plasmid that controls the luciferase activity is lymphoid specific. That means it is only active in lymphoid cells, controlling the expression of lymphoid-specific genes. It works because the correct combination of transcription factors and other regulatory proteins are present in lymphoid cells to bind to the promoter and make it active. This means the promoter can express the luciferase gene.

If it was inserted into kidney cells, the promoter would not be active. The correct combination of regulatory proteins would not be present, and would not be able to turn on the promoter. Therefore, luciferase would not be active.