Schematic depiction of the yeast-two-hybrid screen process using scFv as bait. A. The cDNA of selected scFv is fused to the DNA binding domain of Gal4 (BD) and expressed in yeast as bait. A population of haploid yeast cells harboring short cDNA fragments fused to the activation domain of Gal4 (AD) is then used for mating. Positive clones showing interaction between bait and prey are selected through the expression of a reporter gene. (TM, Transcription Machinery). B. The Predicted Biological Score (PBS) is computed as described before  based on a statistical model of the competition for bait binding between fragments. For practical purposes, numerical numbers are converted to categories A through E as depicted. C. All fragments encoding for the same target ORF are aligned. This yields a selected interacting domain (SID), which narrows the area containing the antibody's binding epitope.