MOLECULAR-CLONING AND SEQUENCING OF EQUINE INHIBIN-ALPHA CDNA

A cDNA probe for recombinant human inhibin a subunit was used to scree n an equine testis cDNA library. Approximately 220,000 plaques were sc reened and 10 positive clones were identified. The largest of these cl ones, approximately 1 kb, was sequenced. The sequence (993 nucleotides [nt]) contained the ARG-ARG proteolytic processing site that precedes the N-terminus of the a subunit mature peptide. The sequence that fol lowed this processing site was 402 nt in length and encoded for a prot ein of 134 amino acids. Nucleotide homology was 88%, 87%, 88%, 82% and 86% with the a subunit cDNA of cattle, pigs, sheep, mice and humans, respectively. Amino acid homology within the mature peptide region was 99%, 88%, 92%, 87% and 86% with the a subunit of cattle, pigs, sheep, mice and humans, respectively. The equine a subunit peptide contained 6 cysteine residues and one potential N-glycosylation site (Asn-Ile-S er). The estimated molecular weight of the amino acid sequence for the mature protein was 14.7 kDa. The equine inhibin a subunit cDNA was us ed as a probe on a Northern blot of total RNA from various horse tissu es. Positive hybridization (1.6 kb) was observed in the adrenal, corpo ra lutea from mares 55 and 100 days pregnant, and testis RNA, but not in the kidney, muscle, small intestine, liver from mares 55 and 100 da ys pregnant, epididymis or lung.