Interferon sequence homology and receptor binding activity of ovine trophoblast antiluteolytic protein

Sequencing of the 40 N-terminal amino acids of the blastocyst protein responsible for blocking corpus luteum regression in early pregnancy in sheep revealed a 37% homology with human alpha-interferon; 28% of the remaining amino acid changes were conservative. 125I-Labelled human alpha-interferon bound to membrane receptors from sheep uteri with an approximate Kd of 4 x 10(-11) M; binding was inhibited by unlabelled alpha-interferon or purified blastocyst antiluteolytic protein. The blastocyst antiluteolytic protein therefore closely resembles the interferon-alpha family of antiviral proteins.