CLONING AND SEQUENCE-ANALYSIS OF A PITUITARY PROLACTIN CDNA FROM THE BRUSHTAIL POSSUM (TRICHOSURUS-VULPECULA)

Overlapping cDNA partial clones of pituitary prolactin from the marsup ial brushtail possum (Trichosurus vulpecula) were isolated and sequenc ed. The nucleotide and deduced amino acid sequences showed high sequen ce identity with pig prolactin (84.3 and 92.5%, respectively) and all of the expected structural features of a quadruped prolactin. A prolac tin gene tree was constructed and rates of evolution calculated for po ssum along with several mammalian and nonmammalian prolactins. Possum prolactin was most closely linked to the prolactins of eutherian mamma ls but branched from the main mammalian line well before the eutherian prolactins. The prolactin/GH family shows variable rates of evolution ranging from 0.3 substitutions/amino acid site/year x 10(9) for pig p rolactin to 7.0 substitutions/amino acid site/year x 10(9) for the mou se. Since divergence from the eutherian mammals, possum prolactin has shown a slow rate of evolution (0.2 substitutions/amino acid site/year x 10(9)). As expected, the prolactin gene was expressed in the possum pituitary gland but not in the liver, lung, kidney, heart, or mammary gland. (C) 1998 Academic Press.