Methods for identifying novel secreted mammalian polypeptides

A method for identifying a secreted mammalian protein comprising the steps of:

• a) constructing a mammalian cDNA library;
• b) inserting the cDNA library of step (a) into a signal trap vector to generate a signal trap library, wherein the vector comprises DNA encoding a reporter polypeptide, the reporter polypeptide being a secreted mammalian growth factor lacking a functional signal sequence;
• c) amplifying the signal trap library of step (b);
• d) transfecting the library of step (c) into a mammalian host cell lacking a functional reporter polypeptide of step (b);
• e) selecting transfected mammalian host cells from step (d) for growth in selective medium requiring secretion of the reporter polypeptide;
• f) analyzing the DNA recovered from the transfected cells of step (e) which exhibit growth on selective medium to determine whether a functional mammalian signal sequence is present and;
• g) screening a mammalian cDNA library to identify a full-length cDNA comprising the functional mammalian signal sequence of step (f), wherein the cDNA encodes a secreted mammalian protein.