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A hybrid construct derived from ovine trophoblastin cDNA and bovine α-lactalbumin-encoding gene, was injected into the pronuclei of mouse eggs. In one of the resulting transgenic mouse lines, expression of the hybrid construct was detected and found to be limited to the mammary gland of lactating females which secreted active ovine trophoblastin. This strongly suggests that important cis-acting DNA sequences involved in tissue-specific expression of the bovine gene are located within the second half of the 3′ untranslated region, or/and the proximal 5′and 3′ regions flanking the transcriptional unit.

CrystalX‐ray crystallographyThree‐dimensional structureTb3+ParvalbuminCa2+‐binding site

Ovine trophoblastic protein B (oTPB), an embryonic protein, is a 20 kDa secretory protein which is synthesized by the ovine conceptus from days 12 to 22 of pregnancy. oTPB was purified by HPLC using ion-exchange chromatography on a DEAE column and was subsequently chromatographed on a reversed-phase column. Automated Edman degradation was then used to determine the N-terminal amino acid sequence up to 45 residues. The sequence data reveal a significant homology between oTPB and bovine interferons α of class II: 64% of the amino acids are identical and 75% are homologous. A highly conserved region including residues 23–44 exhibits 82% homology. Identity between oTPB and either HuIFN-α.9 or MuIFNα. 1 is 55%. These alignments between oTPB and IFNs occur at the N-terminus of the mature proteins and proceed without deletion. These results suggest that oTPB is an embryonic interferon.