Characterization of the fusion cDNA produced by 15D3 cells. (A) Predicted structure of the mutant fusion protein. The neuropilin-1 protein and the mutant protein are shown. SS, signal sequence; TM, transmembrane domain. a1, a2, b1, b2, and MAM are previously described neuropilin-1 sub-domains.42 (B) Portion of the sequence obtained by 5′ RACE, displaying the fusion between neuropilin-1 and gene trap vector sequences. 642 is the last codon of neuropilin-1 sequences and 220 is the first codon of En-2 sequences present in the trap vector.