A single-copy relaxin-like gene sequence is present in sheep

Relaxin is a peptide hormone which consists of two polypeptide chains that are synthesized as a B-chain/C-peptide/A-chain precursor. We have used the polymerase chain reaction (PCR) to isolate and clone a relaxin-like cDNA from sheep placental RNA. This cDNA and two sheep genomic clones were characterised by nucleotide sequencing. A comparison of the sheep nucleotide sequence with exon II of pig relaxin revealed homology of 72%. The sheep sequence had numerous stop codons in the region corresponding to the C-peptide. Therefore, there is no open reading frame which would include the C-peptide and A-chain regions. Analysis of several animals indicates that the stop codons are not due to an allelic polymorphism and Southern blot analysis of genomic DNA reveals the presence of a single copy gene. The 5' RACE PCR protocol was used to obtain sequence information for the 5' relaxin-like RNA. This analysis reveals that unprocessed precursor RNA is the predominant RNA species in placenta. A small proportion of clones was isolated which contained novel 5' sequences. These sequences mostly appear to be generated from repetitive DNA elements upstream of exon II. No relaxin-like exon I sequence which encodes the B-chain was found after an extensive search of the 5' RACE PCR products. Therefore, this relaxin-like gene does not produce an RNA species in ovary, placenta or endometrial tissue which could give rise to a functional sheep relaxin hormone.