Abstract: Provided is a genetically modified non-human mammal that comprises an anchor DNA sequence inserted at an endogenous locus of a secretory milk protein gene, wherein the anchor DNA sequence comprises a site-specific recombinase recognition site. Also provided is a genetically modified non-human mammal that comprises a transgene inserted at an endogenous locus of a secretory milk protein gene, wherein the transgene encodes a secretory protein and is operably linked to the endogenous promoter of said secretory milk protein gene, and wherein the transgene is flanked by a pair of site-specific recombinase resulting sites. The genetically modified non-human mammals provided can be used for producing the secreted recombinant protein encoded by the transgene from the milk produced by the genetically modified non-human mammals.

Abstract: Provided is a method of inserting a polynucleotide sequence into a genome of a cell. The method comprises: generating a double-strand break at a target site of the genome; and introducing into the cell a virus. The virus comprises a nucleic acid comprising the polynucleotide sequence to be inserted or the complementary sequence thereof. The nucleic acid does not comprise a homologous arm or comprises very short (5˜25 bp) homologous arms corresponding to the target site. Also provided herein is a composition for inserting a polynucleotide sequence into a genome of a cell. The composition comprises a site-specific nuclease capable of generating a DNA double-strand break at a target site of the genome and a virus comprising a nucleic acid comprising the polynucleotide sequence or the complementary sequence thereof.