Cellular growth defects triggered by an overload of protein localization processes

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• High-level expression of proteins targeting specific cellular compartments is predicted to cause defects by overwhelming localization machinery.
• Systematic studies on the overload of these protein localization processes are lacking.

Purpose of the Study:

• To systematically investigate the cellular consequences of overexpressing proteins with localization signals.
• To identify the limiting factors and cellular defects associated with overloaded protein localization pathways.

Main Methods:

• Utilized budding yeast as a model system.
• Expressed various green fluorescent proteins (GFPs) with distinct localization signals at high levels.
• Assessed cellular defects and correlated them with protein expression levels and localization pathway function.

Main Results:

• High-level expression of localized GFPs was limited similarly to toxic misfolded GFPs, causing defects.
• The expression limit for nuclear export signal-tagged GFPs was determined by exportin Crm1 availability.
• Misfolding of vesicle-transported GFPs induced ER stress but did not solely limit expression; mitochondrial targeting signal precursors caused defects.

Conclusions:

• Overexpression of localized proteins leads to cellular defects by exceeding the capacity of cellular localization processes.
• The study quantifies the residual capacities of these essential cellular transport systems.
• Identifies specific molecular players, like Crm1, that dictate expression limits in localization pathways.