Sheep thyroxine-binding globulin: cDNA sequence and expression.

A full-length thyroxine-binding globulin clone was isolated from a sheep liver cDNA library. The nucleotide sequence consisted of 1379 nucleotides and contained the coding region of 1236 nucleotides. The deduced sequence of the mature protein was 396 amino acids long. The similarity of the sheep thyroxine-binding globulin amino acid sequence with those of human and rat were 80% and 76%, respectively. Expression of the thyroxine-binding globulin gene was investigated by Northern analysis. The gene was not expressed in choroid plexus nor at other extrahepatic sites. The expression of the thyroxine-binding globulin gene was also studied during sheep foetal development. Thyroxine-binding globulin mRNA was already detected in livers of 1 cm long foetuses and levels similar to those found in liver from adult sheep were reached half way through pregnancy.