The concentration of a particular protein, X, in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply.The level of its mRNA in the cell remains fairly constant throughout this time.Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed.You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal.Which of the following mutations in the gene for X could explain these results?

Question

Quizplus · Accepted Answer

The deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein would prevent the degradation of protein X, leading to abnormally high levels throughout the cell cycle and the inability to undergo cell division despite normal levels of mRNA.

The Concentration of a Particular Protein, X, in a Normal