BioVector® pYE22m Yeast Expression and Heterologous Complementation Vector / pYE22m 酵母高表达与功能互补鉴定穿梭质粒

I Product General Information and Molecular Background

• Plasmid Nomenclature: pYE22m.

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

  The pYE22m plasmid is a specialized, high-performance cloning platform designed for synthetic biology, plant physiology, and functional genomics. It is widely recognized as a benchmark tool for the heterologous expression and functional characterization of membrane transporters (e.g., potassium channels, sucrose carriers, amino acid permeases, and organic acid transporters) within mutant strains of the budding yeast Saccharomyces cerevisiae.

• Core Expression Elements and Regulatory Architecture:

  • Promoter (Constitutive Expression Drive): Driven by a robust, truncated variant of the yeast $pGAP$ (Glyceraldehyde-3-phosphate dehydrogenase) constitutive promoter. This guarantees continuous, high-level transcription of cloned target genes across all phases of cell division without requiring costly or toxic chemical inducing agents (such as galactose or copper ions).

  • Yeast Replication Origin: Powered by the $2\mu\text{ origin}$ ($2\mu\text{ ori}$). This element allows the plasmid to maintain a high-copy status within the yeast cytoplasm ($10 - 40$ copies per cell), overcoming the low-yield limitations associated with single-copy integration vectors.

  • Yeast Selection Coordinate (Auxotrophic Marker): Outfitted with a functional $URA3$ gene encoding orotidine-5'-phosphate decarboxylase. This enables direct positive selection in uracil-auxotrophic yeast mutant lineages (e.g., strains grown on Synthetic Defined media lacking uracil, SD-Ura).

• Bacterial Shuttle Backbone Coordinates:

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

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

  • Total Vector Dimensions: Spans approximately 5,400 to 5,800 bp depending on the exact multiple cloning site (MCS) variant configuration.

II Strategic Research Value and Functional Complementation Assays

The pYE22m platform is highly valued in transporter biology and plant molecular genetics for its stability and high expression levels:

1. Characterization of Plant and Fungal Membrane Transporters:

   Many plant transport proteins, such as potassium inward-rectifying channels (AKT1/AKT2), nitrate transporters (NRT families), and ammonium transporters (AMT), are difficult to study in standard proteobacterial hosts. By inserting these eukaryotic open reading frames (ORFs) into pYE22m and transforming them into specialized yeast strains, researchers can measure transport mechanics, substrate affinities ($K_m$), and ion selectivities.

2. Yeast Mutant Complementation and Phenotypic Rescue Assays:

   • Potassium Transport Mapping: Transformed into the potassium-uptake-deficient yeast mutant CY162 (which lacks endogenous high-affinity $K^+$ transporters like TRK1 and TRK2). If the cloned gene is functional, the pYE22m-Transporter construct will rescue CY162 growth on low-potassium media ($1 - 5\ \text{mM}\ K^+$), whereas the empty pYE22m-empty control will fail to grow.

   • Amino Acid Permease Tracking: Transformed into mutant lines (e.g., the 22$\Delta$10$\alpha$ strain, which lacks multiple amino acid transport pathways) to characterize the substrate profiles of novel plant or fungal amino acid permeases.

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 pYE22m 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 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 sample must be free from genomic DNA, RNA, or chemical carryover. 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 (~5.5 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 pYE22m construct into uracil-auxotrophic yeast mutants (e.g., CY162), execute the standard Lithium Acetate protocol:

1. Starter Culture Preparation: Inoculate the target yeast strain into a permissive medium (e.g., YPD broth supplemented with 100 mM KCl for potassium mutants) and grow at 30 °C with shaking overnight.

2. Log-Phase Harvesting: Back-dilute the starter culture into fresh permissive medium 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 pYE22m 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. (Adjust this duration based on the sensitivity of the specific mutant strain being used).

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 uracil (SD-Ura), supplemented with any additional nutrients required by the specific mutant line.

8. Incubation: Incubate the plates inverted at 30 °C for 3 – 5 days until distinct $URA3^+$ prototrophic transformant colonies appear.

4. Downstream Complementation Monitoring and Quality Control

• Experimental Controls: Always run three parallel control strains during functional verification: Wild-type yeast, the mutant strain transformed with the empty pYE22m vector, and the mutant strain transformed with the recombinant pYE22m-Transporter construct.

• Assay Tuning: For functional screens (e.g., checking potassium uptake), harvest the transformants from the SD-Ura plates, wash them with sterile water to remove residual ions, and spot serial dilutions ($10^{-1}$ to $10^{-4}$) onto SD-Ura agar plates containing varying concentrations of the target substrate. Monitor growth at 30 °C for 48–72 hours to confirm functional complementation.

5. Long-Term Cryopreservation Parameters

• Cryoprotectant Preservation Formula: 70% sterile SD-Ura 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-Ura 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 constitutive promoter.

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