2) To study protein localization signals you engineered a yeast strain that lacks two non- essential genes: 1) DNAide and Timolase. replaced each endogenous gene with recombinant forms that encode modified localization signals. A) DNAide is critical for DNA repair following damage by UV light. The encoded amino acid sequence of each localization signal within the modified DNAide gene is indicated in MMS FVSLLLVGILFWTA.. the figure to the right. Predict how expression of the modified protein will impact yeast viability following exposure to UV light. Be sure to NA TT COOH justify your answer in the context of where the modified protein will NH localize within the cell. (4 points) KKKRK. B) Timolase is normally localized inside the mitochondria where it helps to maintain proper H balance. This enables sufficient energy production for cell growth when yeast are exposed to acidic environments. The localization signals for the MLSLROSIRFFKPATRTLCSSRYLL.... modified Timolase gene indicated in the figure to the right. Predict L COOH how yeast growth will be impacted when cultures are grown NH Timolase media. Be sure to justify your answer in the i pH 3 modified context of where the KDEL (4 points protein will localize within the cell. (4 points) Solution Answer: 2. (A) KKKRK is a nuclear localization signal (NLS) and proteins containing this sequence are imported into the cell nucleus through nuclear transport. Thus, the modified DNAide containing the KKKRK sequence will be localized in the nucleus. So, it can act as a DNA repair protein upon DNA damage following UV exposure and help the cell to survive. (B) KDEL sequence when present prevents the secretion of proteins from the endoplasmic reticulum (ER). It can also target proteins from other sites to the ER and can leave the ER only when the sequence is removed. The protein timolase is present inside the mitochondria and help maintain H+ balance. The modified protein contains the KDEL sequence which targets and limits the modified timolase to the ER. Thus, the protein can no longer maintain the H+ balance in the cell. At acidic pH of 3, most of the proteins and enzymes inside the cell gets denatured. This may lead to intracellular acidification and ultimately death of the cells by the ROS pathway..

1. 2) To study protein localization signals you engineered a yeast strain that lacks two non-
essential genes: 1) DNAide and Timolase. replaced each endogenous gene with recombinant
forms that encode modified localization signals. A) DNAide is critical for DNA repair following
damage by UV light. The encoded amino acid sequence of each localization signal within the
modified DNAide gene is indicated in MMS FVSLLLVGILFWTA.. the figure to the right.
Predict how expression of the modified protein will impact yeast viability following exposure to
UV light. Be sure to NA TT COOH justify your answer in the context of where the modified
protein will NH localize within the cell. (4 points) KKKRK. B) Timolase is normally localized
inside the mitochondria where it helps to maintain proper H balance. This enables sufficient
energy production for cell growth when yeast are exposed to acidic environments. The
localization signals for the MLSLROSIRFFKPATRTLCSSRYLL.... modified Timolase gene
indicated in the figure to the right. Predict L COOH how yeast growth will be impacted when
cultures are grown NH Timolase media. Be sure to justify your answer in the i pH 3 modified
context of where the KDEL (4 points protein will localize within the cell. (4 points)
Solution
Answer:
2. (A) KKKRK is a nuclear localization signal (NLS) and proteins containing this sequence are
imported into the cell nucleus through nuclear transport.
Thus, the modified DNAide containing the KKKRK sequence will be localized in the nucleus.
So, it can act as a DNA repair protein upon DNA damage following UV exposure and help the
cell to survive.
(B) KDEL sequence when present prevents the secretion of proteins from the endoplasmic
reticulum (ER). It can also target proteins from other sites to the ER and can leave the ER only
when the sequence is removed.
The protein timolase is present inside the mitochondria and help maintain H+ balance. The
modified protein contains the KDEL sequence which targets and limits the modified timolase to
the ER. Thus, the protein can no longer maintain the H+ balance in the cell.
At acidic pH of 3, most of the proteins and enzymes inside the cell gets denatured. This may lead
to intracellular acidification and ultimately death of the cells by the ROS pathway.