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The 2 micron plasmid: a selfish genetic element with an optimized survival strategy within Saccharomyces cerevisiae
Syed Meraj Azhar Rizvi1, Hemant Kumar Prajapati1, Santanu Kumar Ghosh2
1Department of Biosciences and Bioengineering, Indian Institute of Technology, Bombay, Powai, Mumbai, 400076, India.
Abstract:
Since its discovery in the early 70s, the 2 micron plasmid of Saccharomyces cerevisiae continues to intrigue researchers with its high protein-coding capacity and a selfish nature yet high stability, earning it the title of a 'miniaturized selfish genetic element'. It codes for four proteins (Rep1, Rep2, Raf1, and Flp) vital for its own survival and recruits several host factors (RSC2, Cohesin, Cse4, Kip1, Bik1, Bim1, and microtubules) for its faithful segregation during cell division. The plasmid maintains a high-copy number with the help of Flp-mediated recombination. The plasmids organize in the form of clusters that hitch-hike the host chromosomes presumably with the help of the plasmid-encoded Rep proteins and host factors such as microtubules, Kip1 motor, and microtubule-associated proteins Bik1 and Bim1. Although there is no known yeast cell phenotype associated with the 2 micron plasmid, excessive copies of the plasmid are lethal for the cells, warranting a tight control over the plasmid copy number. This control is achieved through a combination of feedback loops involving the 2 micron encoded proteins. Thus, faithful segregation and a concomitant tightly controlled plasmid copy number ensure an optimized benign parasitism of the 2 micron plasmid within budding yeast.
Insights
The 2 micron plasmid in Saccharomyces cerevisiae is a stable, selfish genetic element. It uses host factors and its own proteins for replication and segregation, maintaining a controlled copy number to ensure survival.
Area of Science:
- * Molecular and Cellular Biology
- * Yeast Genetics
- * Epigenetics
Background:
- * The 2 micron plasmid of Saccharomyces cerevisiae is a high-copy number plasmid known for its stability and selfish genetic nature.
- * It encodes essential proteins (Rep1, Rep2, Raf1, Flp) for its maintenance and segregation.
- * The plasmid relies on host factors for its replication and faithful partitioning during cell division.
Purpose of the Study:
- * To elucidate the mechanisms underlying the stable, high-copy number maintenance of the 2 micron plasmid.
- * To understand the interplay between plasmid-encoded proteins and host factors in plasmid segregation.
- * To investigate the regulatory mechanisms controlling 2 micron plasmid copy number.
Main Methods:
- * Analysis of plasmid-encoded proteins and their interactions with host factors.
- * Investigation of Flp-mediated recombination in plasmid maintenance.
- * Study of host factors (e.g., microtubules, motor proteins) involved in plasmid segregation.
Main Results:
- * The 2 micron plasmid utilizes plasmid-encoded proteins (Rep1, Rep2) and host factors (microtubules, Kip1, Bik1, Bim1) for chromosome hitchhiking and segregation.
- * Flp-mediated recombination is crucial for maintaining the high-copy number of the plasmid.
- * Tight control over plasmid copy number is achieved through feedback loops involving plasmid-encoded proteins, preventing lethal over-replication.
Conclusions:
- * The 2 micron plasmid exemplifies a 'miniaturized selfish genetic element' with optimized benign parasitism.
- * Faithful segregation and precise copy number control are key to the plasmid's persistence in budding yeast.
- * Understanding these mechanisms provides insights into selfish genetic element dynamics and host-parasite interactions.
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