To obtain a protein and a gene encoding it, which each serve as an effective therapeutic agent for diseases caused by death of nerve cell and function to restrain the death of nerve cell or accelerate growth of nerve cell.

This inhibitory factor is a protein having an amino acid sequence of the formula or a gene encoding the protein. The gene is obtained by culturing a rat PC12 cell transformed by a bc12 gene in a proper medium to obtain a protein PCTF35 having an activity to restrain death of cell, synthesizing an oligonucleotide of a base sequence which is assumed on both an amino acid sequence up to the N-terminal 21-residue of the protein and a N-terminal amino acid sequence of a limited decomposition obtained by breaking peptide chains of PCTF35 by cyanogen bromide, and cloning a gene pctf35 encoding PCTF35 from a cDNA library prepared from a mRNA prepared from a pc12 cell according to a PCR method using the synthesized oligonucleotide as a probe.