To provide a new natural fiber material with excellent physical properties. Any one of the following nucleic acids (a) to (d): (a) a nucleic acid having a base sequence of SEQ ID NO: 1 or 19 (b) a nucleic acid encoding a protein having an amino acid sequence of SEQ ID NO: 2 or 20 (c) a nucleic acid encoding a dragline protein and having a sequence identity of 90% or more with the nucleic acid (a) (d) a nucleic acid which encodes a dragline protein and hybridizes with a complementary chain of the nucleic acid (a) under stringent conditions.
