The growth hormone-binding protein in rat serum is an alternatively spliced form of the rat growth hormone receptor.

A cDNA clone isolated from rat liver was demonstrated to encode a soluble, secreted growth hormone (GH)-binding protein consistent with the properties of the newly discovered serum GH-binding protein. The protein coding region of this cDNA was identical in sequence to the extracellular domain of the rat liver GH receptor up to three amino acids before the putative transmembrane domain. At this point, an additional 17 amino acids were encoded in the GH-binding protein before a stop codon was encountered. This cDNA clone was shown to be representative of the structure of the mRNA present in rat liver. These results suggest that the mechanism for production of the rat serum GH-binding protein is by alternative splicing of the gene for the rat GH receptor.