High homology between a trophoblastic protein (trophoblastin) isolated from ovine embryo and α‐interferons

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Abstract
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.