Analysis of the interaction between single-chain variable fragments and their antigen in a reducing intracellular environment using the two-hybrid system.

The coding sequences of three single-chain variable (scFv) fragments (A4, G4 and H3), which bind to dihydroflavonol-4-reductase (DFR) of Petunia hybrida, and the DFR-encoding sequence were cloned in two-hybrid vectors. The vectors were transformed in the yeast strain HF7c (his3-200, trp1-901, leu2-3) and the scFv-DFR interaction was analyzed by measuring yeast growth on medium without histidine. ScFv-G4 and, to a lesser extent, scFv-A4 could interact with DFR in the yeast nucleus. On the contrary, scFv-H3 showed no interaction with its antigen in yeast. The results of a previous expression analysis of the same scFv fragments in the plant cytosol correlate with those of the two-hybrid test. This suggests that it is possible to evaluate the antigen-scFv interaction in a reducing subcellular environment with the two-hybrid test. Therefore, the yeast two-hybrid system can be useful to identify candidate scFv fragments for intracellular antibody applications.