The anchoring of protein R to the cytosolic face of the plasma membrane is due to a post-translational modification of t

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The Anchoring Of Protein R To The Cytosolic Face Of The Plasma Membrane Is Due To A Post Translational Modification Of T 1 (54.59 KiB) Viewed 174 times

The Anchoring Of Protein R To The Cytosolic Face Of The Plasma Membrane Is Due To A Post Translational Modification Of T 2 (45.16 KiB) Viewed 174 times

The anchoring of protein R to the cytosolic face of the plasma membrane is due to a post-translational modification of the protein. Extracellular signals are responsible for protein R activation. Protein R can only be activated when it is bound to GTP. This activation allows yeast cells to grow. Yeast cells stop to grow when there is no extracellular signal and protein Ris inactivated. Protein Ris inactivated when GTP is hydrolyzed into GDP and a protein triggers the replacement of GDP by GTP. At this state protein R could be activated again if the correct extracellular signals are present. You know that two other proteins, M and S, interact with each other, and that only one of them has a post- translational modification responsible for its anchorage to the plasma membrane. In wild-type and mutant strains of yeast, an analysis of the intracellular localization of proteins R, M and S gives the following results. Yeast strain (growing Protein M Proteins Protein R temperature) Wild type (37°C, and 25°C) membrane membrane membrane Mut 1 (37°C, and 25°C) cytoplasm cytoplasm membrane Mut 2 (25°C) membrane membrane membrane Mut 2 (37°C) membrane cytoplasm membrane The gene coding for protein M is mutated in strain Mut 1, and the gene coding for protein Sis mutated in strain Mut2.

c) Two plasmids PM and ps were designed to drive the expression of proteins M and respectively in yeast. In both plasmids, a multiple cloning site allows the insertion of DNA coding for different proteins of interest. The resulting recombinant plasmids (pM-X, PM-Y and pS-X) drive the expression of fusion proteins M-X, M-Yor, S- X. The mut2 strain is co-transformed with different combinations of plasmids (pM, PS, PM-X, P-M-Yand pS-X) and the growth of the transformed colonies is tested at 25°C and 37 °C. The results of these experiments are shown below. Growth at 25°C Growth at 37°C Proteins expressed by the plasmids SM S-X, M-X S-X, M S-X, M-Y Yes Yes Yes No Yes No Yes No Briefly explain these results, and state why this method can be described as a type of yeast two-hybrid system for membrane proteins. Note that this variant of the two-hybrid system does not involve DNA binding domains or transcription activating domains (10 pts).