Introduction to Yeast Transformation

History of Transformation & Transformation in Yeast

Yeasts are eukaryotic model systems for studies as they exhibit fast growth and have dispersed cells. They have a well-defined genetic system and a highly versatile DNA transformation system that can be utilized effectively for protein production.

Transformation is the process by which exogenous DNA is introduced into a cell, resulting in an inheritable change or genetic modification. This was first reported in Streptococcus pneumoniae by Griffith in 1928.¹ The principle of DNA transformation was demonstrated by Avery et al. in 1944.² In the case of fungi, the spheroplasts of the budding yeast Saccharomyces cerevisiae were first successfully transformed in 1978.³

In the case of fungi, the spheroplasts of the budding yeast Saccharomyces cerevisiae were first successfully transformed in 1978.³ Most species of yeast, including Saccharomyces cerevisiae, may be transformed by exogenous DNA in the environment.⁴ Yeast cells are treated with enzymes to degrade their cell walls, yielding spheroplasts. These cells are very fragile but take up foreign DNA at a high rate.⁵ Recombinant DNA technology in yeast has established itself, and a multitude of different vector constructs are available.

Transformation in a Cell

Several methods of transformation in yeast cells (Figure 1) have been developed.^{4, 5} Some of the common methods used in transformation of yeast cells are lithium, electroporation, biolistic and glass bead methods. These methods are commonly used for S. cerevisiae but can be used for transforming other fungi such as yeasts (e.g., Schizosaccharomycespombe, Candida albicans and Pichiapastoris) and filamentous fungi (e.g., Aspergillus species).

Requirements

Transformation method involves three main steps:

• Preparing competent yeast cells
• Transformation with plasmid DNA
• Subsequent plating to select the transformants.

Review materials required and the detailed protocol of transformation.

Applications

Transformation is widely used in molecular biology. Some of the common uses of yeast transformation are as follows:

• Yeast transformants can be used further for cell lysis and plasmid preparation purposes.
• The plasmid DNA obtained from the transformants can be then used as PCR templates or for the transformation of E. coli.
• Yeast transformants are used in yeast two-hybrid systems to study protein-protein or protein-DNA interactions.
• Yeast transformation techniques can also be used for the commercial manufacture of proteins and enzymes.
• They are also used in the food industry and plant waste disposal systems.
• Yeast expression systems designed for the synthesis and secretion of human proteins (like interleukin-1β) may have immense therapeutic potential in the pharmaceutical industry.

Calculation of Transformation Efficiency

Various species of yeast have different efficiencies.⁶ The transformation efficiency is defined as the number of transformants generated per µg of supercoiled plasmid DNA used in the transformation reaction.⁷ Most of the transformation protocols have been developed for baker's yeast, S. cerevisiae and may not be ideal for other species.

Factors Affecting Efficiency

Some of the factors affecting the efficiency of yeast transformation are as follows:

• Size of DNA
• Plasmids
• Forms of DNA
• Cell genotype
• Cell growth
• Type of transformation