Different forms of the prolactin receptor insights into the mechanism of prolactin action.

The primary structure of two forms (short [ approximately 300 amino acids] and long [ approximately 600 amino acids]) of prolactin (PRL) receptor have been deduced by cloning their cDNAs. PRL receptors belong to the superfamily of cytokine growth hormone-PRL receptors, based on conserved sequences in their extracellular domains. No clear second messenger of PRL has been identified, and because of the wide range of actions associated with PRL, it is doubtful that a single unifying mechanism will be found. Mutagenesis of extracellular and intracellular domains of the PRL receptor should help define subdomains involved in hormone binding, and coupled with a functional assay, delineate regions necessary for signal transduction.