The present invention relates to conjugate of Interferon covalently linked to a polymer such polyethylene glycol predominantly at the lysine residue to the protein, wherein preferentially, one polymer strand gets linked to one interferon molecule. The conjugate is attached at the lysine such as at the positions of Lys31, Lysl21/134, Lysl33, Lysl31, Lysl64, Lysl21, Lys83 and Lysll2 of the interferon molecule. The conjugation of the PEG at lysine is achieved by the novel process of production and purification of interferon. The conditions of this novel and inventive process allow the interferon to conjugate at the lysine residue the processes include production, purification of interferon and dialysis during the purification of interferon.
