DEVELOPMENTALLY-REGULATED EXPRESSION OF A PUTATIVE PROTEASE INHIBITORGENE IN THE LACTATING MAMMARY-GLAND OF THE TAMMAR WALLABY, MACROPUS-EUGENII

A novel milk protein, which is secreted only in the early stage of lac tation, has been identified in the whey fraction of milk from the tamm ar wallaby (Macropus eugenii). The amino acid sequence currently avail able suggests the protein comprises 71 amino acids. The protein migrat es at 18 kDa when analysed by SDS polyacrylamide gel electrophoresis b ut has a calculated molecular weight of 8 kDa. A partial cDNA clone of 153 bp has been isolated by reverse transcriptase PCR. Northern analy sis of mammary gland RNA extracted from various stages throughout the entire lactation period showed a messenger RNA transcript of approxima tely 500 bp present only in the first third of lactation. The protein shares 74.5% similarity at the amino acid level with early lactation p rotein (ELP) from the brush-tailed possum (Trichosurus vulpecula) and 37% with bovine colostrum trypsin inhibitor, a member of the Kunitz fa mily of protease inhibitors. We hypothesise that the expression of thi s gene may be controlled by changes in the sucking patterns of the dep endent pouch young. (C) 1998 Elsevier Science Inc. All rights reserved .