RECEPTOR DOMAINS INVOLVED IN SIGNAL-TRANSDUCTION OF PROLACTIN AND GROWTH-HORMONE

Prolactin (PRL) and growth hormone (GH) receptors are members of a sup erfamily that include receptors for a number of cytokines. GH and its receptor form an unusual homodimer consisting of one molecule of GH an d two molecules of receptor. A similar homodimer of the PRL receptor i s probably required for biological effects to be seen. Using specific assays to measure the functional activity of PRL and GH receptors, a 2 5 amino acid juxtamembrane region has been identified as essential but not sufficient for normal action. More detailed studies have limited the region to eight amino acids, rich in prolines, that is highly cons erved in many members of the receptor superfamily. Finally, GH and PRL have been shown to induce the rapid tyrosine phosphorylation of an as sociated kinase, Janus kinase 2, and of the receptor itself.