Cloning and analysis of the cDNA for the common alpha-subunit of the donkey pituitary glycoprotein hormones

Reverse transcription-PCR was used to clone the coding donkey (Equus asinus) glycoprotein hormone alpha-subunit transcript from pituitary gland RNA. The donkey alpha-subunit sequence demonstrated considerable identity with the horse (97% at the nucleotide level), confirming the very close evolutionary linkage between these two species. The predicted amino acid sequence revealed that the donkey alpha-subunit has the same unusual C-terminus as the horse alpha-subunit, when compared with all other mammalian alpha-subunits, including a Tyr-His transposition between positions 87 and 93 and Ile instead of Ser as the C-terminal residue. Since recent evidence indicates important involvement of this region of the alpha-subunit in receptor binding, these findings provide a possible partial explanation for the unique biological properties of the equine gonadotrophins.