In vivo production of cyclic peptides

A retroviral vector comprising a nucleotide sequence encoding a fusion polypeptide comprising, from N-terminus to C-terminus:

• a) a C-terminal domain of an intein;
• b) a peptide;
• c) an N-terminal domain of an intein;
• wherein the amino acid sequence of said intein or region thereof is obtained from a bacteria or yeast and wherein said fusion protein is capable of undergoing a reaction to cyclize said peptide to produce a cyclic peptide in a mammalian cell.

A retroviral vector comprising a nucleotide sequence encoding a fusion polypeptide comprising, from N-terminus to C-terminus:

• a) a C-terminal domain of an intein;
• b) a random peptide;
• c) an N-terminal domain of an intein;
• wherein the amino acid sequence of said intein or a region thereof is obtained from Synechocystis and wherein said fusion protein is capable of undergoing a reaction to cyclize said peptide to produce a cyclic peptide in a mammalian cell.