cDNA cloning of growth hormone from the brushtail possum (Trichosurus vulpecula)

The full-length nucleotide sequence for the cDNA of growth hormone (GH) from the marsupial brushtail possum (Trichosurus vulpecula) was determined using reverse transcription followed by polymerase chain reaction (RT-PCR) and the 5'/3' rapid amplification of cDNA ends (RACE) technique. Sequence information showed that the possum GH cDNA was 831 base pairs (bp) in length, including the 5'untranslated region (60 bp), the signal peptide (75 bp), the mature protein (573 bp, including stop codon), and the 3' untranslated region (123 bp). At both the nucleotide and the amino acid level (deduced from nucleotide sequence), there was a high degree of sequence identity with pig and horse. These species were similar at 82.8 and 83.0% of bases at the nucleotide level and 91.6 and 91.1% at the amino acid level, respectively. Northern analysis showed that GH mRNA is present in the pituitary gland and was similar in size to that seen in other mammals (approximately equal to 0.9 kb). Analysis of molecular evolution of GH in the possum indicated that the rate of evolution is relatively slow (0.4 substitutions/ amino acid site/year x 10(9) and typical of that seen for nonprimate mammals, which exhibit rates ranging between 0.2 and 1.3 substitutions/amino acid site/year x 10(9).