The tre oncogenic locus was identified in transformants receiving human DNA from Ewing's sarcoma cells EW1. Genetic elements of tre originate from chromosomes 5, 18, and 17. The TRE17 oncogene is consistently transcribed in various human cancer cells and proves oncogenic (onc) in expression vector-based assays. Here, the nucleotide sequence of TRE17 with defined noncoding and two coding exons (4,426 nucleotides) was compared with sequences cloned from placental DNA library or generated by polymerase chain reaction (PCR) from EW1 and independent healthy individuals. Cloned sequences displayed restriction site polymorphism, with different patterns for EW1 and normal tissues. Sequence analysis revealed that they originate from a family of homologous sequences alpha, beta, and gamma. TRE17 alpha and less frequent TRE17 beta (similarity score approximately equal to 88%) were found in both normal and EW1 cells. oncTRE17, classified as TRE17 beta, differed from the wild-type TRE17 beta, besides a few intronic changes, by a single-base frameshift insertion in one of the coding exons. TRE17 gamma, so far identified in EW1 but not in normal somatic cells, diverged from oncTRE17 by 6% nucleotide substitutions and by stop codons in each reading frame. The results are consistent with the possibility that TRE17 sequences other than oncTRE17 are translated if alternatively spliced. Expression of TRE17 in normal somatic cells was, however, not yet reported.