Expression vector and method for producing protein

1. An expression vector comprising an expression cassette containing a structural gene sequence (y) encoding a protein (Y), a structural gene sequence (z) located downstream from the structural gene sequence (y) and encoding a protein (Z) that is a protein to be recovered, and a promoter sequence and a terminator sequence for expressing a fusion protein containing the protein (Y) moiety and the protein (Z) moiety,

wherein the protein (Y) is

a partial protein of PDI1 comprising an endoplasmic reticulum (ER) targeting signal, a PDI1 a-domain, a PDI1 b-domain, and a PDI1 x-domain,

wherein said ER targeting signal is followed by a PDI1 a-domain, a PDI1 b-domain, and a PDI1 x-domain and wherein said PDI1 b-domain and said PDI1 x-domain are directly fused to one another in the order of PDI1 b-domain-PDI1 x-domain, or

a partial protein of PDI1 comprising an endoplasmic reticulum (ER) targeting signal, a PDI1 a-domain, a PDI1 b-domain, a PDI1 b′-domain, and a PDI1 x-domain, and which does not contain either one of a PDI1 a′-domain or a PDI1 c-domain,

wherein said ER targeting signal is followed by a PDI1 a-domain, a PDI1 b-domain, a PDI1 b′-domain, and a PDI1′ x-domain.

2. The expression vector according to claim 1 , wherein the protein (Y) has an endoplasmic reticulum targeting signal of PDI1.

3. The expression vector according to claim 1 , wherein the PDI1 is PDI1 from yeast, PDI1 from filamentous fungus, or PDI1 from human.

4. The expression vector according to claim 1 , further comprising a structural gene sequence (w), in between the structural gene sequence (y) and the structural gene sequence (z), encoding a cleavage site (W) that is comprised of an amino acid or a peptide and functions as a site to be cleaved at the N-terminal side of the protein (Z) moiety either in inside or outside of a cell.

5. The expression vector according to claim 4 , wherein the cleavage site (W) is a site to be cleaved at the N-terminal side of the protein (Z) moiety of the fusion protein in inside of a cell.

6. The expression vector according to claim 5 , wherein the cleavage site (W) is KR (K: lysine, R: arginine), or a peptide comprised of at least three amino acids and has KR at its C-terminal side that binds to the protein (Z) moiety.

7. The expression vector according to claim 4 , wherein the cleavage site (W) is a site recognized by a protease that can cleave the N-terminal side of the protein (Z) moiety of the fusion protein.

8. A method for producing a transformant, characterized in that the expression vector as defined in claim 1 is introduced into a host cell.

9. A transformant comprising the expression vector as defined in claim 1 as an extrachromosomal gene.

10. A transformant comprising the expression cassette of the expression vector as defined in claim 1 in a chromosome.

11. A method for producing a protein, comprising cultivating the transformant as defined in claim 9 and recovering the fusion protein or the protein (Z) from a culture broth obtained by cultivation.

12. A method for producing a protein, comprising cultivating the transformant as defined in claim 10 and recovering the fusion protein or the protein (Z) from a culture broth obtained by cultivation.

13. A method for producing a protein, comprising cultivating a transformant having the expression cassette of the expression vector as defined in claim 7 in a chromosome or having the expression vector as defined in claim 7 as an extrachromosomal gene, recovering the fusion protein from a culture broth obtained by cultivation, and cleaving the N-terminal side of the protein (Z) moiety of the fusion protein by means of a protease to produce the protein (Z).

14. A cloning vector comprising a promoter sequence capable of functioning in a host cell, a structural gene sequence (y) encoding a protein (Y) located downstream from the promoter and regulated by the promoter, a cloning site located downstream from the structural gene sequence (y) for introducing a structural gene, and a terminator sequence capable of functioning in the host cell,

wherein the protein (Y) is

a partial protein of PDI1 comprising an endoplasmic reticulum (ER) targeting signal, a PDI1 a-domain, a PDI1 b-domain, and a PDI1 x-domain,

wherein said ER targeting signal is followed by a PDI1 a-domain, a PDI1 b-domain, and a PDI1 x-domain and wherein said PDI1 b-domain and said PDI1 x-domain are directly fused to one another in the order of PDI1 b-domain-PDI1 x-domain, or

a partial protein of PDI1 comprising an endoplasmic reticulum (ER) targeting signal, a PDI1 a-domain, a PDI1 b-domain, a PDI1 b′-domain, and a PDI1 x-domain, and which does not contain either one of a PDI1 a′-domain or a PDI1 c-domain,

wherein said ER targeting signal is followed by a PDI1 a-domain, a PDI1 b-domain, a PDI1 b′-domain, and a PDI1 x-domain.

15. The expression vector according to claim 1 , wherein the protein (Y) is a partial protein of PDI1 comprising an endoplasmic reticulum (ER) targeting signal, a PDI1 a-domain, a PDI1 b-domain, and a PDI1 x-domain,

wherein said ER targeting signal is followed by a PDI1 a-domain, a PDI1 b-domain, and a PDI1 x-domain and wherein said PDI1 b-domain and said PDI1 x-domain are directly fused to one another in the order of PDI1 b-domain-PDI1 x-domain.

16. The expression vector according to claim 1 , wherein the protein (Y) is a partial protein of PDI1 comprising an endoplasmic reticulum (ER) targeting signal, a PDI1 a-domain, a PDI1 b-domain, a PDI1 b′-domain, and a PDI1 x-domain, and which does not contain either one of a PDI1 a′-domain or a PDI1 c-domain,

wherein said ER targeting signal is followed by a PDI1 a-domain, a PDI1 b-domain, a PDI1 b′-domain, and a PDI1 x-domain.