mRNA translation in yeast during entry into stationary phase

Area of Science:

• Molecular Biology
• Cell Biology
• Yeast Genetics

Background:

• Gene expression in Saccharomyces cerevisiae shifts as cells enter stationary phase.
• Stationary phase translation occurs when the translational machinery is less active.
• This raises questions about mRNA competition for limited translation factors.

Purpose of the Study:

• To investigate how different 5'-leaders affect mRNA translation during yeast growth and stationary phase.
• To determine if mRNAs compete differently for translation factors under varying growth conditions.

Main Methods:

• Comparison of lacZ mRNA translation with various 5'-leaders (PYK1, PGK1, RpL3, Rp29, HSP12, HSP26, THI4).
• Analysis of mRNA translatability during exponential growth and stationary phase (glucose starvation).
• Polysome profiling to assess translation efficiency of specific mRNAs (PYK1, ACT1, HSP26) and levels of translation initiation factors (eIF-2alpha, eIF-4E, eIF-4A).

Main Results:

• Relative translational efficiencies of mRNAs with different 5'-leaders remained consistent between exponential and stationary phases.
• Wild-type PYK1, ACT1, and HSP26 mRNAs were translated efficiently during stationary phase.
• Sufficient levels of key translation initiation factors (eIF-2alpha, eIF-4E, eIF-4A) were maintained throughout the growth cycle.

Conclusions:

• Yeast mRNAs with different 5'-leaders compete effectively for translation factors even in stationary phase.
• Yeast cells possess excess translational capacity during stationary phase, despite reduced overall translational activity.
• This ensures continued protein synthesis for essential genes during periods of stress or nutrient limitation.