The mammary gland-specific expression systems developed by the present inventors, named pGbc, pGbc_L and pGbc_S were deposited under the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the Purpose of Patent Procedure in the Korean Collection for Type Cultures (KCTC), Korean Research Institute of Bioscience and Biotechnology at 52, Oun-dong, Yusong-Ku, Taejon 305 333, Republic of Korea, on Aug. 17, 1998, and the accession deposit Nos. KCTC 0515BP, 0514BP and 0513BP were issued, respectively. All restructions on the availability to the public of the deposited materials will be irrevocably removed upon the granting of a patent. The systems of the present invention make it possible that desired proteins are produced by expression in mammary gland tissue-derived animal cells or through the milk secreted from the transgenic animals with the expression systems, thereby solving the above-mentioned problems, that is, the activity sustenance, production cost, and isolation and purification of the desired proteins.