DNA which comprises an amino acid sequence containing any one of the following amino acid sequences (a) to (c) and encodes a protein, said protein having an activity of allowing a non-natural amino acid to bind to phenylalanine-specific tRNA, and a transgenic silkworm characterized by having a promoter which enables silk gland-specific expression of the aforesaid DNA: (a) an amino acid sequence having a mutation in the position corresponding to amino acid No. 432 of the amino acid sequence represented by SEQ ID NO: 1; (b) an amino acid sequence derived from the aforesaid amino acid sequence (a) by deletion, insertion, substitution or addition of one to several amino acids in position(s) other than the position corresponding to amino acid No. 432; and (c) an amino acid sequence having at least 80% identity with the aforesaid amino acid sequence (a) in positions other than the position corresponding to amino acid No. 432.
