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.[Key Words: Growth hormone; receptor; binding protein]Received April 27, 1989; revised version accepted June 7, 1989. Growth hormone (GH) is a polypeptide secreted by the anterior pituitary that acts through specific high-affinity cell-surface receptors located primarily in the liver (Hughes and Frieson 1985). Recently a specific high-af finity protein that binds GH has been identified in serum (Ymer and Herington 1985;Baumann et al. 1986;Herington et al. 1986). This serum GH-binding protein has a close structural relationship to the GH receptor present on the surface of cells. Genetic, immimological, and biochemical data suggest colinearity and identity between the extracellular domain of the GH receptor and the GH-binding protein (Eshet et al. 1985;Barnard and Waters 1986; Baumaim et al. 1987;Daughaday and Trivedi 1987;Leung et al. 1987; Baumann and Shaw 1988;Spencer et al. 1988). It has been proposed that the GH-binding protein is produced by proteolytic cleavage of the GH receptor (Leung et al. 1987;Spencer et al. 1988;Trivedi and Daughaday 1988).We now report the isolation and characterization of two classes of cDNA clones, both of which encode pro teins that bind GH in vitro. One class encodes a mem brane-bound protein, which is the GH receptor. The other class of cDNA clones encodes a soluble secreted protein that contains the same putative GH-binding re gion but lacks the transmembrane and intracellular do mains. These regions are replaced with a 17-amino-acid hydrophilic segment that is followed by a unique 3'-un translated region. The data suggest that the serum GHbinding protein in rats is likely to be an alternatively spliced form of the GH receptor. 'Corresponding author. ^Present address: Embryogen, Princeton Forrestal Center, Princeton, New Jersey 08540 USA. Results Isolation and characterization of GH receptor and GHbinding protein cDNAsTo isolate clones that encode the rat GH receptor, a rat liver cDNA library was screened with two oligonucleo tide probes and a fragment of a rabbit GH receptor cDNA. On the basis of restriction mapping and prelimi nary DNA sequence analysis, the clones could be sepa rated into two classes. Two clones, RatRl and RatBPl, as representatives of each class, were sequenced com pletely. Figure 1 shows the nucleotide se...

The interaction of activated Ras with Raf initiates signaling cascades that contribute to a significant percentage of human tumors, suggesting that agents that specifically disrupt this interaction might have desirable chemotherapeutic properties. We used a subtractive forward two-hybrid approach to identify small molecule compounds that block the interaction of Ras with Raf. These compounds (