Methods, compositions and systems for production of recombinant spider silk polypeptides

An isolated nucleic acid that encodes a spider silk fibroin polypeptide or an analog of a spider silk fibroin polypeptide, operably linked to at least one silkworm fibroin nucleic acid sequence, wherein the silkworm is Bombyx mori, Bombyx mandarina, Antheraea peryni, or Antheraea yamamai;

• wherein the at least one silkworm nucleic acid sequence comprises a 5′ end of a native silkworm fibroin gene, a 3′ end of a native silkworm fibroin gene, or both a 5′ end of a native silkworm fibroin gene and a 3′ end of a native silkworm fibroin gene;
• wherein the analog of the spider silk fibroin polypeptide is encoded by a nucleic acid sequence comprising at least 2800 nucleotides encoding alternating beta-sheet domains and alpha-helix domains, wherein the amino acid sequence of the beta-sheet domains are each at least 60% identical to at least one of the betasheet domains as set forth in SEQ ID NO:
• 2, and wherein the analog of the spider silk fibroin polypeptide is at least 50% stronger than native silkworm silk.