Cross-Species Transmission of Plasmids in Saccharomyces Yeast

Saccharomyces yeast carry native plasmids that are 6,000 bp circular molecules of double stranded DNA found in the nucleus. They are called 2-micron plasmids and are parasitic by nature, using host cell processes to replicate and spread. We use the 2-micron plasmid as a model system to study cross species transmission of parasitic genetic elements. Different 2-micron plasmids can be found in the species S. cerevisiae, S. paradoxus and S. eubayanus. We hypothesize that evolutionary differences within 2-micron plasmids will influence their ability to replicate and segregate within different species of yeasts. ELT3 is a plasmid that is structurally similar to the native S. cerevisiae plasmid, but has been engineered to contain a selectable genetic marker that we can use to observe the stability of the plasmid over time in the laboratory. We have created two new 2-micron plasmids derived from S. paradoxus and S. eubayanus with engineered selectable markers, and will use them to study the stability of these plasmids within different species of yeast. This system can be used to study interspecies transmission of plasmids as a model to study how viruses invade new species, such as HIV jumping from primate to human hosts