Isolation and Characterization of a Complementary DNA Clone for a Mr 32,000 Protein Which Is Induced with Tumor Promoters in BALB/c 3T3 Cells1

The synthesis of a protein of M, 32,000 (p32) is enhanced by various tumor promoters, chemical carcinogens, metal salts, and heat shock in BALB/c 3T3 cells. We have isolated a complementary DNA (cDNA) clone for p32 from a XgtlO library of BALB/c 3T3 cells. The library was constructed from mRNA extracted from the cells treated with sodium arsenite, which stimulates the p32 expression most effectively among various agents so far tested. Having screened this library differentially with probes which represent induced and uninduced mRNA populations for p32, we first obtained a partial p32 cDNA clone and have subsequently succeeded in the isolation of a cDNA clone containing the entire coding sequence. RNA blot analysis has shown that p32 mRNA is induced as early as 0.5 h after the addition of 12-O-tetradecanoyl-phorbol-13-acetate or sodium arsenite. Computer-assisted comparison with GenBank data has revealed a striking similarity in the nucleotide sequences between cDNAs of p32 and rat heme oxygenase. These results strongly suggest that p32 is a mouse homolog of this enzyme.