Abstract: Transgenic animals capable of expressing a desired protein can be prepared by co-introducing into an egg or embryo cell of an animal, a first sequence, which encodes the desired protein, and a second, more efficiently expressed, DNA sequence. Expression efficiency is thereby conferred on the first sequence, leading to improved yield or targeting, or both. Co-introduction may be achieved by co-injecting a mixture of the two DNA sequences into a fertilized egg, in the case of an animal. The invention can be used to enhance the efficiency of expression of desired proteins, such as those having pharmaceutical activity in the mammary gland of a female transgenic animal.

Abstract: A method of producing a substance comprising a peptide, involves incorporating a DNA sequence coding for the peptide into a gene of a mammal (such as a sheep) coding for a milk whey protein in such a way that the DNA sequence is expressed in the mammary gland of the adult female mammal. The substance may be an (optionally modified) protein such as a blood coagulation factor. The DNA sequence is preferably inserted into the first exon of a gene coding for a whey protein such as beta-lactoglobulin. The substance will generally be recovered from milk of the female mammal, but may (for example if it is an enzyme) be used in situ.