The Stability of the Zeocin Resistance Marker in P. pastoris

The yeast Pichia pastoris is used for the heterologous expression of many valuable proteins. For instance, proteins such as human prion protein and insulin have been successfully produced in this yeast. In order to transform Pichia pastoris with a foreign gene, one must utilize a selectable marker gene to identify cells which have successfully brought in the foreign gene. The zeocin resistance gene is a common marker that is used for the transformation of Pichia pastoris. The zeocin resistance gene encodes a protein that confers onto a cell the ability to degrade zeocin. Thus, cells that have picked up the zeocin resistance gene can grow on media that contains this antibiotic. It is accepted that the zeocin gene stably integrates into a yeast chromosome and is stable for many generations. We have carried out a study to determine how stable the zeocin resistance gene is in transformed Pichia pastoris. In our experiments, cells containing the zeocin resistance gene were grown for varying amounts of time on nonselective media and then switched back to medium containing zeocin. This experiment should help in our understanding of the fate of the zeocin resistance gene in Pichia pastoris