Immunoglobulin frameworks that demonstrate improved stability in the intracellular environment and methods for identification

A frame of single chain variable fragment (scFv fragment) having the general structure: NH2-VL-linker-VH-COOH; or NH2-VH-linker-VL-COOH wherein the VL domain has the framework sequence SEQ ID NO. 4 and the VH domain has the sequence under SEQ ID NO. 11, the scFv framework is stable under reducing conditions.