Slide 28 -
(a) A bifurcated cellular pathway will have distinct networks on genetic- and physical interaction maps. Proteins A, B, C and D (blue) and proteins 1, 2, 3, and 4 (green) are members of two functionally redundant pathways required to perform an essential function. Proteins A, B and C interact with each other physically, so do proteins 1, 2 and 3.
(b) A protein interaction map, or physical interaction map, identifies interactors based on protein-protein interactions.
(c) A genetic interaction map identifies interactors based on functions without the requirement that the proteins must interact. The combination of these two complementary approaches can be used to deduce a cellular pathway and, in principle, enable the construction of a wiring diagram of the yeast cell. Genetic versus physical interaction maps One way to reveal the functions of the remaining nonessential genes and to identify essential processes is to perform a systematic genome-wide synthetic-lethality analysis.
Synthetic lethality describes any combination of two separately non-lethal mutations that leads to inviability, whereas synthetic sickness indicates a combination of two separate non-lethal mutations that confers a growth defect more severe than that of either single mutation.
The interpretation is that synthetic sickness reflects an important genetic interaction, whereas synthetic lethality reflects an essential interaction.