Sequence for a OneSTrEPtag (OST), two STOP codons, a loxP site, the mouse Ace (angiotensin I converting enzyme (peptidyl-dipeptidase A) 1) promoter, the cre recombinase gene, a neomycin resistance gene cassette, and a second loxP site were inserted in-frame at the 3 end of the gene coding sequence in exon 13. Cre-mediated self-excision removed the selection cassette in the male germline. The fusion of the OST to the protein can be used in affinity purification. (J:209882)