In mammals the structure of pituitary GH is generally strongly conserved, indicating a slow basal rate of molecular evolution. However, on two occasions, during the evolution of primates and of artiodactyls, the rate of evolution has increased dramatically (25- to 50-fold) so that the sequences of human and ruminant GHs differ markedly from those of other mammalian GHs. In order to define further the burst of GH evolution that occurred in artiodactyls we have cloned and characterised the GH gene of red deer (Cervus elaphus) using genomic DNA and a polymerase chain reaction technique. The deduced sequence for the mature GH from red deer is identical to that of bovine GH, indicating that the burst of rapid evolution of GH that occurred in Artiodactyla must have been completed before the divergence of Cervidae and Bovidae and suggesting that the rate of evolution during this burst must have been greater than previously estimated. In other aspects (signal sequence, 5' and 3' sequences, introns and synonymous substitutions in the coding sequence) the red deer GH gene differs considerably from the GH genes of other ruminants. Differences between the signal peptide sequences of red deer and bovid GHs probably explain why N-terminal heterogeneity is seen in bovine, ovine and caprine GHs but not GH from red deer, pig or most other mammals.
A Lioupis, E Nevo and M Wallis
In mammals the structure of pituitary GH is generally strongly conserved, reflecting a slow basal rate of molecular evolution. However, on a few occasions the rate has increased - markedly during the evolution of primates and artiodactyls, and to a small extent during the evolution of rodents and rabbit - giving rise to marked differences between GH sequences of these species. In order to extend knowledge of rodent GHs we have cloned and characterised part of the GH gene of the Eurasian mole rat (Spalax ehrenbergi) using genomic DNA and a PCR technique. The sequence of all of the coding region and 5' untranslated region (UTR), most of the 3' UTR and part of the promoter region is described. The overall organisation of the mole rat GH gene is similar to that of GH genes from other mammals. The proximal Pit-1 sequence in the gene promoter differs somewhat from that of rat or mouse. The deduced sequence for the mature GH from mole rat differs from that of pig GH (thought to be identical to the ancestral placental mammal GH sequence) at 7 residues and from rat, mouse and hamster GHs at 9 to 12 residues. Only one or two of these substitutions involve residues close to the receptor-binding sites of the hormone.