Equine (e) CG and LH beta-subunits have identical amino acid sequences, including an extended carboxyl-terminal peptide (CTP). This suggests that unlike the corresponding human genes, the beta-subunits of eCG and eLH may be encoded by a single gene and share a common proximal promotor region. To explore this, we isolated and characterized the eLH/CG beta gene(s). Data from Southern analyses suggest that the eCG beta and eLH beta subunits are products of the same single copy gene (eLH/CG beta). Overlapping fragments of the eLH/CG beta gene and cDNA were amplified from equine genomic DNA and pituitary gland mRNA by the polymerase chain reaction, cloned, and sequenced. The eLH/CG beta gene spans less than 1.2 kilobase-pairs and has three exons that translate a CTP-containing polypeptide identical in sequence to that previously reported for the mature equine protein. There is, however, little amino acid homology shown between the CTP of human or equine CG beta subunit. In addition, unlike the human genes, the same TATAA-like element appears to be involved in directing initiation of transcription of the eLH/CG beta gene in placenta and anterior pituitary. Based upon these differences, we suggest that the CG beta genes evolved independently in humans and equids and that different mechanisms are involved in their patterns of placenta-specific expression.

No abstract

Neither gene locus nor gene sequence characterizations have been reported for the subunits of guinea pig (gp) LH and putative gp chorionic gonadotropin (CG). Descriptions of this locus would allow comparison with functionally relevant molecular genetic features of other species' homologous loci including the single-copy equid LH/CG gene and the primate LH -CG gene cluster locus. Contiguous cDNA and genomic DNA fragments spanning the entire mature coding sequence of gpLH mRNA, gpCG mRNA and a homologous gpLH/CG gene were amplified using PCR methodologies. With the exception of one silent mutation, the two cDNA and the genomic sequences were identical where they overlapped. Comparison of guinea pig coding sequence with LH , CG and LH/CG sequences of other vertebrate species revealed the following order of similarity expressed as per cent coding sequence identity: rhinoceros LH (83·6%)>pig LH (81·8%)>donkey LH/CG =bovine LH (81·5%)> horse LH/CG (80·6%)>dog LH (79·7%)>human LH (78·2%)>rat LH (77·9%)>human CG (75·8%)>turkey LH (52·7%); values that are generally consistent with recently postulated phylogenetic relationships. Like the consensus mammalian LH gene, the 5 -flanking region of the gpLH/CG gene contains a single TATA sequence 37 bp upstream of the translation start codon. The first in-frame stop codon occurred at codon position +122 which is consistent with the 121 amino acid residue length of the consensus mammalian mature LH peptide.

No abstract