Wilms' tumor, a pediatric nephroblastoma, has been associated with genetic alterations of the 11p13 and 11p15 regions. The introduction of a der(11) chromosome into the G401 Wilms' tumor cell line has been shown previously to revert the tumorigenic phenotype. A subtractive cDNA/RNA hybridization performed between the tumorigenic parent (G401) and a nontumorigenic microcell hybrid of G401 (110.1/G401.1) containing the der(11) chromosome resulted in the identification of a single novel cDNA clone, designated QM. The cDNA is 745 nucleotides in length and encodes a predicted hydrophilic 25 kd basic protein, primarily consisting of alpha helices. The QM transcript is expressed in a wide variety of embryonic and adult tissues and demonstrates a down regulation of expression in adult kidney and heart. QM is also a member of a multigene family members of which map to chromosomes 6 and 14. The QM mRNA level is modulated between the tumorigenic and nontumorigenic cell lines and therefore may be involved in the maintenance of the nontumorigenic phenotype.