Methods for protein synthesis, protein screening and retrieval of protein function

A method for protein screening comprising:

• adding to a cell-free extract solution a template gene prepared by subjecting the nucleotide sequence of nucleic acid encoding an arbitrary protein with intermolecular and/or intramolecular disulfide bonds to a specific or random modification;
• synthetically preparing the protein encoded by the template gene using the cell-free extract solution;
• and screening the synthetically prepared protein by assaying the activity thereof.

A retrieval method for protein function comprising:

• adding to a cell-free extract solution a template gene encoding an arbitrary protein requiring the formation of a specific pattern of intermolecular and/or intramolecular disulfide bonds for the expression of a function, wherein at least a part of the function is unknown;
• synthetically preparing the protein encoded by the template gene using the cell-free extract solution;
• and retrieving the unknown function of the protein by testing the function of the prepared protein.