Recombinant multicopy plasmids in yeast - interactions with the endogenous 2µm.

Area of Science:

• Molecular Biology
• Yeast Genetics
• Recombinant DNA Technology

Background:

• Flp-mediated recombination drives amplification of the endogenous 2µm plasmid in Saccharomyces cerevisiae.
• High copy numbers of YEp-type vectors are crucial for research and industrial applications.
• Mechanisms for YEp-type plasmid amplification in yeast are not fully elucidated.

Purpose of the Study:

• To investigate the mechanisms of YEp-type plasmid amplification in yeast.
• To analyze the structural alterations of YEp-type plasmids in Saccharomyces cerevisiae.
• To identify recombination events contributing to high-copy-number plasmid maintenance.

Main Methods:

• Cultivation of yeast strains with six isomeric YEp-type model expression plasmids under varying conditions.
• Back transformation of shuttle vectors into Escherichia coli for analysis.
• High-resolution analysis of 586 ampicillin-resistant (ampR) clones to detect plasmid structural changes.

Main Results:

• Approximately 11% of analyzed plasmids showed structural alterations, indicating a lower limit of recombination events.
• Two main recombination categories were observed: Flp-based and Flp-independent.
• Flp-based recombination involved intermolecular events with the 2µm plasmid, potentially mediating amplification.
• Flp-independent homologous recombination led to plasmid oligomerization, even in 2µm-free strains.

Conclusions:

• Both Flp-mediated and Flp-independent homologous recombination contribute to YEp-type plasmid structural variations in yeast.
• These recombination pathways are critical for achieving and maintaining high plasmid copy numbers.
• The gene of interest and its expression can influence host physiology beyond plasmid maintenance sequences.