The invention features a method for identifying a cDNA nucleic acid encoding a mammalian protein having a signal sequence, which method includes the following steps: (a) providing library of mammalian cDNA; (b) ligating the library of mammalian cDNA to DNA encoding alkaline phosphatase lacking both a signal sequence and a membrane anchor sequence to form ligated DNA; (c) transforming bacterial cells with the ligated DNA to create a bacterial cell clone library; (d) isolating DNA comprising the mammalian cDNA from at least one clone in the bacterial cell clone library; (e) separately transfecting DNA isolated from clones in step (d) into mammalian cells which do not express alkaline phosphatase to create a mammalian cell clone library wherein each clone in the mammalian cell clone library corresponds to a clone in the bacterial cell clone library; (f) identifying a clone in the mammalian cell clone library which expresses alkaline phosphatase; (g) identifying the clone in the bacterial cell clone library corresponding to the clone in the mammalian cell clone library identified in step (f); and (h) isolating and sequencing a portion of the mammalian cDNA present in the bacterial cell library clone identified in step (g) to identify a mammalian cDNA encoding a mammalian protein having a signal sequence.
Nucleic acid molecules encoding a secreted neural adhesion protein