Relative Quantitation of Protein–Protein Interaction Strength Within the Yeast Two-Hybrid System via Fluorescence β -Galactosidase Activity Detection in a High-Throughput and Low-Cost Manner

The yeast two-hybrid (Y2H) method is capable of delivering vast amounts of interacting positive yeast colonies from a single library screen, particularly if a multifunctional protein is used as bait. However, the selection of definitive colonies for further molecular analysis is limited by both technical practicality and high costs. Here we demonstrate a cost-effective and simple method for the rapid selection and ranking of those Y2H-positive interaction clones that are suitable for further analysis. We performed a Y2H screen for the identification of human transforming growth factor β2- interacting proteins in a human skin keratinocyte library. The identified clones were ranked by the amount of β-galactosidase enzyme produced, as well as by the interaction strength of the positive colonies. The combination of high-throughput microplate fluorescence readers and specific fluorescence assays can be utilized for relative quantitation of protein–protein interaction strength of Y2H-positive colonies in crude yeast-cell lysates. We demonstrate here that the high sensitivity of the fluorescence approach can bypass cumbersome conventional methods of cell lysis used in β-galactosidase assays, and still deliver accurate values for analysis of protein interaction data. Finally, we also achieved a better understanding of general aspects of β-galactosidase measurements in the Y2H system, such as protein normalization, the influence of yeast culture incubation time on optimalβ-galactosidase detection, and the linearity of β-galactosidase detection in crude cell lysates.