BioVector® pYX222 High-Copy Yeast Expression Vector / pYX222 高拷贝酵母表达穿梭质粒

I Product General Information and Molecular Background

• Plasmid Nomenclature: pYX222 (Often referenced as pYX222x within modular expression series).

• Vector Class and Target Expression Framework: High-Copy Yeast Expression Shuttle Vector.

  The pYX222 plasmid is a high-performance cloning vehicle engineered for synthetic biology, metabolic engineering, and functional genomics. It is widely utilized as a standard platform for the high-level, constitutive heterologous expression of recombinant proteins, enzymes, and metabolic pathways within the budding yeast Saccharomyces cerevisiae.

• Core Expression Elements and Regulatory Architecture:

  • Promoter (Constitutive Expression Drive): Driven by a powerful, truncated variant of the yeast $pTPI$ (Triosephosphate isomerase) constitutive promoter. This promoter guarantees continuous, high-efficiency transcription of cloned target genes across both the exponential growth phase and the stationary phase without requiring the addition of chemical inducing agents (such as galactose, copper, or doxycycline).

  • Yeast Replication Origin: Powered by the $2\mu\text{ origin}$ ($2\mu\text{ ori}$). This replication origin ensures autonomous, high-copy episomal maintenance within the yeast cytoplasm ($10 - 40$ copies per cell), making it ideal for maximizing protein yields or driving metabolic flux.

  • Yeast Selection Coordinate (Auxotrophic Marker): Outfitted with a functional $HIS3$ gene encoding imidazoleglycerol-phosphate dehydratase. This enables direct positive selection in histidine-auxotrophic yeast host lineages (e.g., transgenic strains cultivated on Synthetic Defined media lacking histidine, SD-His).

• Bacterial Shuttle Backbone Coordinates:

  • E. coli Origin: Employs a high-copy pUC-derived replication origin (\textit{ori}) to facilitate high-density plasmid propagation, sequence verification, and downstream cloning assembly within standard Escherichia coli cloning hosts.

  • Bacterial Selective Pressure: Outfitted with the $\beta$-lactamase gene imparting Ampicillin resistance ($Amp^R$), standardly selected in bacterial cultures using a working concentration of $100\ \mu\text{g/mL}$.

  • Total Vector Dimensions: Spans approximately 5,200 to 5,600 bp depending on the exact multiple cloning site (MCS) variant configuration.

II Strategic Research Value and Synthetic Biology Applications

The pYX222 platform is highly valued in industrial biotechnology and fungal genetics due to its high-copy maintenance and robust promoter activity:

1. Heterologous Enzyme Overproduction:

   Widely implemented to express heavy-duty industrial enzymes (e.g., cellulases, amylases, and lipases) or plant-derived secondary metabolic enzymes in yeast factories. The constitutive $pTPI$ promoter allows for continuous accumulation of target proteins throughout the fermentation cycle.

2. Metabolic Pathway Engineering:

   In multi-gene metabolic engineering strategies (such as the reconstruction of terpenoid, flavonoid, or biofuel pathways), pYX222 serves as a reliable expression cassette for enzymes requiring high baseline activity. It operates seamlessly alongside compatible low-copy (CEN/ARS) plasmids or vectors with alternative auxotrophic markers ($URA3$, $TRP1$, $LEU2$).

3. Yeast Functional Complementation Assays:

   Used to overexpress foreign genes to rescue metabolic defects in specific histidine-auxotrophic or corresponding functional mutant yeast strains, helping researchers rapidly confirm enzyme function in vivo.

III Laboratory Bacterial Cloning, Quality Control, and Yeast Transformation Protocols

1. Plasmid Amplification and High-Purity Isolation in E. coli

• Recommended Competent Host Strain: Escherichia coli DH5$\alpha$, Top10, or XL1-Blue.

• Bacterial Selective Pressure Matrix: Supplement standard LB broth or agar with $100\ \mu\text{g/mL}$ Ampicillin.

• Propagation Workflow:

  1. Introduce 1 $\mu$L of pYX222 plasmid DNA (empty vector or recombinant construct) into a 50 $\mu$L aliquot of competent DH5$\alpha$ cells.

  2. Incubate on ice for 30 minutes, heat-shock at 42 °C for 45 seconds, and place back on ice for 2 minutes.

  3. Add 250 $\mu$L of standard SOC or LB broth; recover at 37 °C with shaking at 220 rpm for 45 minutes.

  4. Spread the transformation mixture onto ampicillin-selective LB agar plates and incubate inverted at 37 °C for 14 – 16 hours.

  5. Inoculate an isolated colony into 5 – 10 mL of selective LB broth. Grow at 37 °C with shaking at 250 rpm overnight, and isolate high-purity plasmid DNA using a standard silica-column miniprep kit.

2. Analytical Quality Control Guidelines

Before proceeding to yeast transformation, verify the purity, concentration, and structural identity of the isolated plasmid DNA:

• Purity Thresholds: Measure optical density using a NanoDrop spectrophotometer. Quality Control Standard: Acceptable $OD_{260}/OD_{280}$ ratios must fall between 1.8 and 2.0. The preparation must be free from genomic DNA, RNA, or chemical contaminants. Ensure a concentration threshold $\ge 200\text{ ng/}\mu\text{L}$.

• Restriction Enzyme Fingerprinting:

  Digest the plasmid using diagnostic restriction enzymes that target unique sites within the Multiple Cloning Site (MCS). Resolve the fragments on a 1% agarose gel. Quality Control Band Profile: The empty linearized backbone must migrate as a single, clean band corresponding to its baseline molecular weight (~5.4 kb). Recombinant constructs must cleanly yield the backbone band alongside the distinct insert fragment.

3. Lithium Acetate (LiAc/PEG-3350) Yeast Transformation Protocol

To introduce the pYX222 construct into histidine-auxotrophic yeast strains, execute the standard Lithium Acetate protocol:

1. Starter Culture Preparation: Inoculate the target histidine-auxotrophic yeast strain into standard YPD broth and grow at 30 °C with shaking overnight.

2. Log-Phase Harvesting: Back-dilute the starter culture into fresh YPD broth to an initial $OD_{600}$ of approximately 0.2. Incubate at 30 °C with shaking until the culture reaches an $OD_{600}$ of 0.6 – 0.8 (the ideal window for transformation competence).

3. Cell Conditioning: Centrifuge the yeast cells at 3,000 rpm (~1,000 g) for 5 minutes. Wash the cell pellet with 20 mL of sterile deionized water, pellet again, and resuspend the cells in 1 mL of freshly prepared 0.1 M LiAc solution. Transfer the slurry to a sterile 1.5 mL tube, spin at 12,000 rpm for 20 seconds, and completely aspirate the supernatant.

4. Assembly of the Transformation Cocktail: Add the following components to the yeast pellet strictly in the exact sequence listed:

   • 240 $\mu$L of sterile 50% w/v PEG 3350 solution

   • 36 $\mu$L of sterile 1.0 M LiAc solution

   • 25 $\mu$L of high-concentration Single-Stranded Carrier DNA (e.g., Salmon Sperm DNA, 2 mg/mL, pre-boiled at 95 °C for 5 minutes and immediately chilled on ice)

   • 5 – 10 $\mu$L of purified pYX222 plasmid DNA (~1 – 2 $\mu$g)

5. Homogenization: Mix the dense mixture gently using a pipette tip or light vortexing until the yeast pellet is completely resuspended. Incubate statically at 30 °C for 30 minutes.

6. Heat Shock Application: Transfer the tubes directly into a 42 °C water bath and incubate for exactly 15 – 20 minutes.

7. Plating and Selection: Centrifuge at 12,000 rpm for 30 seconds and carefully remove the PEG/LiAc supernatant. Resuspend the pellet in 100 – 150 $\mu$L of sterile water or sterile saline solution. Spread the suspension onto solid Synthetic Defined (SD) dropout agar plates lacking histidine (SD-His), supplemented with any additional nutrients required by the host line.

8. Incubation: Incubate the plates inverted at 30 °C for 3 – 5 days until distinct $HIS3^+$ prototrophic transformant colonies appear.

4. Downstream Expression Monitoring and Quality Control

• Experimental Controls: Always run standard parallel control strains during validation assays: Wild-type yeast, the host strain transformed with the empty pYX222 vector (Negative Control), and the strain transformed with the recombinant pYX222-Protein construct.

• Expression Analysis: Because the $pTPI$ promoter is constitutively active, protein accumulation can be assessed directly from log-phase liquid cultures grown in SD-His medium. Harvest the biomass, perform total cell lysis using glass beads or enzymatic digestion (Zymolyase), and evaluate protein expression via SDS-PAGE, Western Blotting, or enzymatic activity assays.

5. Long-Term Cryopreservation Parameters

• Cryoprotectant Preservation Formula: 70% sterile SD-His liquid medium blended with 30% sterile analytical-grade Glycerol (yielding a final glycerol concentration of 15% v/v).

• Storage Workflow:

  1. Scrape fresh, healthy yeast transformant colonies from an SD-His plate or harvest a log-phase liquid culture.

  2. Suspend the cells thoroughly in 1 mL of the sterile glycerol cryoprotectant mix inside a sterile cryogenic vial.

  3. Mix by inversion, then transfer the vials directly into a -80 °C ultra-low freezer for long-term storage. Avoid frequent freeze-thaw cycles to prevent plasmid loss or downregulation of the expression system.

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