The hormone somatotropin (growth hormone, GH) which plays an important role in growth control, choriomammotropin (lactogen), a placental analog of GH; and prolactin which acts primarily on the mammary gland by promoting lactation, have been shown [1] to be homologous. This family of proteins also includes other hormones listed below (references are only provided for recently determined sequences).

• Rodents placental lactogens I and II.
• Bovine and sheep lactogen.
• Mouse proliferin I, II, III and proliferin related protein [2].
• Bovine placental prolactin-related proteins I, II, and III [3].
• Rat placental prolactin-like proteins A and B.
• Human growth hormone variants 1 (GH-V1) and 2 (GH-V2).
• Somatolactin (SL) from various fish [4].

The schematic representation of the structure of proteins belonging to this family is shown below.

        <----------------180-to-210-residues------------->
                     ***                          *****
        xxxxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxxxxxxxCxxxCxxC
                     |                            |   |  |
                     +----------------------------+   +--+

'C': conserved cysteine involved in a disulfide bond.
'*': position of the patterns.

We developed two signature patterns for this family of proteins, both patterns include cysteines involved in conserved disulfide bonds.