Yeast Three-Hybrid (Y3H) Service for Advanced RNA-Protein Interaction Screening

Q: What is the difference between Y2H and Y3H?

Y2H detects a direct interaction between two proteins, while Y3H detects an interaction between two molecules (usually proteins) that is mediated or bridged by a third molecule, such as an RNA or a small molecule.

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For over two decades, Creative Biolabs has stood at the forefront of interaction discovery technology. We proudly offer our advanced Yeast Three-Hybrid (Y3H) Service, a powerful in vivo platform designed to identify and characterize transient and stable trimolecular interactions with exceptional sensitivity and reliability. Our state-of-the-art Y3H screening services provide a direct path to understanding the complex interplay between proteins, RNA, and small molecules, driving innovation in drug discovery and fundamental research.

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What is the Yeast Three-Hybrid (Y3H) System?

The Yeast Three-Hybrid (Y3H) system is a sophisticated genetic method derived from the well-established Yeast Two-Hybrid (Y2H) technology. While Y2H is the gold standard for detecting direct protein-protein interactions, the Y3H system is uniquely engineered to detect interactions mediated by a third "bridge" molecule. This third molecule can be either an RNA molecule or a small molecule, making the Y3H system an incredibly versatile tool.

The core principle involves the reconstitution of a functional transcription factor (typically Gal4) in yeast. When the three components—two proteins of interest and a bridging molecule—come together, they activate the transcription of a reporter gene, leading to a detectable phenotype.

Principle of the Yeast Three-Hybrid (Y3H) System

Core Principle

The fundamental principle of the Y3H system relies on the reconstitution of a functional transcription factor in the nucleus of yeast cells. A transcription factor typically consists of two separable domains: a DNA-binding domain (DBD) and a transcription activation domain (AD). Individually, these domains cannot activate reporter gene expression. However, if they are brought into close physical proximity, they can reconstitute a functional transcription factor, leading to the activation of downstream reporter genes.

In the Y3H system, this proximity is achieved not by direct protein-protein interaction, but by an RNA molecule acting as a bridge between two fusion proteins, or by a small molecule acting as a bridge between two proteins.

Components of the Standard Y3H System (for RNA-protein interactions)

"Hook" Fusion Protein: This is typically a fusion between a well-characterized RNA-binding protein (e.g., MS2 coat protein) and a DNA-binding domain (DBD) (e.g., LexA or Gal4-DBD). This "hook" protein binds to a specific RNA sequence (its cognate binding site) and tethers the entire complex to the promoter region of the reporter gene in the yeast nucleus.
"Bait" RNA Molecule: This is a synthetic RNA molecule containing two distinct RNA binding sites:
"Prey" Fusion Protein: This is a fusion between a transcriptional activation domain (AD) (e.g., Gal4-AD) and the protein of interest (Y), which is suspected to interact with the RNA sequence of interest (X).

How it Works (for RNA-protein interactions)

Separate Expression: The three components (Hook-DBD fusion, Bait RNA, and Prey-AD fusion) are introduced into yeast cells on separate plasmids.
Anchoring the Complex: The Hook-DBD fusion protein binds to its specific binding site on the Bait RNA molecule. This effectively tethers the Bait RNA to the reporter gene promoter in the yeast nucleus via the DBD.
Interaction and Reconstitution: If the protein of interest (Y) fused to the AD interacts with the RNA sequence of interest (X) on the Bait RNA molecule, this interaction brings the AD into close proximity with the DBD.
Reporter Gene Activation: The reconstituted functional transcription factor (DBD and AD in close proximity) then drives the transcription of downstream reporter genes. These reporter genes typically confer a selectable phenotype or produce a detectable enzyme.
Detection of Interaction: The activation of the reporter gene serves as an indicator of a positive RNA-protein interaction between RNA X and protein Y.

Y3H system. (OA Literature). Fig.1 General strategy of the Y3H system.¹

Our Advanced Y3H Platforms & Strategies

At Creative Biolabs, we go beyond the standard. We have developed specialized Y3H platforms to meet the most demanding research needs.

NGS-Coupled Y3H (Y3H-Seq)

For unparalleled depth and quantitative analysis, we integrate Next-Generation Sequencing (NGS) with our Y3H screening. Instead of relying solely on colony survival, we use deep sequencing to identify and quantify the frequency of "hit" prey clones.

Advantages:

Higher Sensitivity: Detects low-abundance interactors missed by traditional methods.
Quantitative Data: Provides a ranked list of interactors based on sequence counts.
Reduced False Positives: Statistical analysis of read counts helps eliminate noise.
Ideal for large-scale library-on-library screening.

Reverse Yeast Three-Hybrid (R-Y3H)

While standard Y3H identifies molecules that form a complex, the R-Y3H system is designed to screen for molecules (e.g., small molecules, peptides, or RNA aptamers) that disrupt a pre-existing ternary complex.

Mechanism: A counter-selectable reporter gene (e.g., URA3) is used. When the ternary complex is intact, the yeast dies on a medium containing 5-FOA. A molecule that disrupts the interaction will prevent reporter gene activation, allowing the yeast to survive.
Application: Perfect for high-throughput screening of compound libraries to find inhibitors of essential RNA-protein or protein-protein interactions.

Our Standard Y3H Service Workflow

Step 1: Project Consultation & Design.

We discuss your goals, select the optimal bait/prey/bridge strategy, and design the constructs.

Step 2: Bait & Library Construction.

Cloning of the bait construct and preparation/QC of the prey cDNA library.

Step 3: Yeast Transformation & Mating.

Introduction of bait and prey library constructs into the appropriate yeast strains.

Step 4: High-Throughput Screening.

Plating on dual selective media to identify initial positive colonies.

Step 5: Hit Confirmation & False Positive Elimination.

Re-streaking, control matings, and reporter gene assays (e.g., lacZ) to validate true interactors.

Step 6: Prey Plasmid Isolation & Sequencing.

Identification of the interacting partner proteins by sequencing the prey plasmids from validated positive clones.

Step 7: Data Analysis & Reporting.

Comprehensive bioinformatics analysis and a final, detailed report.

Why Choose Creative Biolabs?

Decades of Experience: Over 20 years of expertise in yeast genetics and interaction screening.
Custom Library Construction: We can construct high-quality cDNA or ORF libraries from any tissue or cell line to ensure the most relevant screening possible.
Multiple Advanced Platforms: Choose from standard, NGS-coupled, or reverse Y3H systems.
Rigorous Quality Control: Every step, from vector construction to hit validation, is subject to stringent QC to minimize false positives and negatives.
Comprehensive Deliverables: You receive a detailed report including a list of validated hits, sequencing data, interaction domain mapping, and full bioinformatics analysis.

We offer a comprehensive, end-to-end Y3H service tailored to your specific project goals. Our expert team works closely with you from experimental design to final data analysis. Other optional protein-nucleic acid interaction (PNI) assay services:

Frequently Asked Questions (FAQ)

Q: What is the difference between Y2H and Y3H?

A: Y2H detects a direct interaction between two proteins. Y3H detects an interaction between two molecules (usually proteins) that is mediated or bridged by a third molecule, such as an RNA or a small molecule.

Q: Can I screen for interactors with a non-coding RNA?

A: Absolutely. Our RNA-bait Y3H system is specifically designed for this purpose. It is one of the most powerful methods available for identifying proteins that bind to a specific lncRNA, miRNA, or other non-coding RNA.

Q: How many clones do you typically screen in a library?

A: We aim to screen at least 1 x 10^7 clones to ensure comprehensive coverage of the library, maximizing the probability of identifying all relevant biological interactors.

Q: How do you handle false positives?

A: We employ a multi-step validation process. Initial hits are re-tested on more stringent selective media. We then perform control experiments, such as testing for auto-activation of the reporter by the bait or prey alone, and often use a second reporter gene (like lacZ) to confirm the interaction.

Q: What do I receive in the final report?

A: You will receive a full project report detailing the entire experimental procedure, raw data, a list of confirmed positive interactors with their DNA sequences and GenBank accession numbers, and a bioinformatics analysis of the hits.

Propel Your Research with Deeper Insights

Don't let the complexity of trimolecular interactions be a barrier to your next breakthrough. Partner with Creative Biolabs to leverage the power of our Yeast Three-Hybrid platform.

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Reference

Czarnecka, Kamila, et al. "New cyclopentaquinoline and 3, 5-dichlorobenzoic acid hybrids with neuroprotection against oxidative stress for the treatment of Alzheimer's disease." Journal of enzyme inhibition and medicinal chemistry 38.1 (2023): 2158822. Under Open Access license CC BY 4.0, without modification. https://doi.org/10.1080/14756366.2022.2158822

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