A yeast expression vector is a tool used to express exogenous genes in yeast cells. It is commonly used in yeast genetic engineering research, leveraging the physiological metabolic characteristics and expression mechanisms of yeast cells to express exogenous genes within them, thereby enabling the efficient expression and purification of target proteins.

    The main components and characteristics of yeast protein expression vectors are as follows:

1. Promoter: A promoter is a sequence that controls the initiation of gene transcription and determines the level of gene expression. In yeast expression vectors, selecting an appropriate promoter is crucial for achieving efficient gene expression.

2. Selection Marker: To ensure that only yeast cells carrying the exogenous gene can survive and replicate, the vector typically contains a selection marker, such as an antibiotic resistance gene. Thus, in a culture medium containing antibiotics, only yeast cells transformed with the expression vector can survive.

3. Multiple Cloning Site (MCS): The MCS is a region containing multiple different restriction enzyme recognition sites, allowing for the easy insertion of exogenous genes. Researchers can select an appropriate site within this region to insert the gene of interest.

4. Terminator: A terminator is a sequence that terminates transcription; it helps ensure that the mRNA of the expressed gene is properly spliced and stabilized.

5. Autonomous Replication Sequence (ARS): This is a sequence that enables the vector to replicate autonomously within yeast cells, ensuring that each cell retains and passes on the exogenous gene.

    Yeast vectors primarily fall into two major categories: Saccharomyces cerevisiae and Pichia pastoris.

    KMD Bioscience uses Pichia pastoris as its host in the development of its yeast secretory expression system, which is a eukaryotic expression system that has developed rapidly and been widely adopted in recent years.

    Pichia pastoris is a methanol-nutrient yeast regulated by the alcohol oxidase (AOX) genes, which are encoded by two genes: AOX1 and AOX2. Among these, AOX1 plays a dominant role in regulating alcohol oxidase activity; since the strain utilizes methanol to produce protein—that is, the synthesis rate is primarily controlled by AOX1— Therefore, methanol strictly regulates AOX1 expression. When only AOX2 is present and AOX1 is absent, alcohol oxidase activity is virtually lost; such cells have a low ability to utilize methanol, and the strain exhibits the Muts phenotype. In the presence of AOX1, cells grow normally using methanol, and this strain exhibits the Mut+ phenotype.

Yeast Protein Expression Vectors:

    Based on the location of the product, yeast expression can be divided into two types: intracellular expression and extracellular expression. This depends on whether a signal peptide is present on the expression vector. In the yeast expression system, the appropriate expression vector is selected primarily based on gene localization and the experimental objective.

(1) Intracellular expression vectors: These mainly include pPIC3, pPICZ, pPSC3K, pHIL-D2, and others. These vectors enable intracellular expression of the target gene while preventing glycosylation of the expressed protein. They are suitable for proteins typically expressed in the cytoplasm or non-glycosylated proteins lacking -S-S- bonds. Compared to extracellular secreted proteins, intracellular expression levels are higher, but purification is relatively cumbersome; furthermore, the protein is generally produced as an inclusion body, requiring an additional renaturation step.

(2) Vectors for extracellular secretion: pPIC9, pHIL-S1, pYAM75P, etc. The signal peptide ensures that the exogenous protein is secreted into the extracellular space and expressed in a soluble form. In addition, this facilitates the purification and accumulation of the target protein.

(3) Multi-copy insertion expression vectors: pPIC9K, pPIC3.5K. As the number of copies increases, so does the protein expression level.