The UBE1L gene isolated from the chromosome 3p21 region has an extremely reduced level of mRNA in lung cancer. Sequence analysis showed a 45% homology to the human ubiquitin-activating enzyme E1 at the amino acid level. To further characterize the protein product, we generated UBE1L protein-specific antibodies. Immunoblot analysis revealed a full-length gene product of approximately 112 kDa. Assessment of the level and distribution pattern of the UBE1L protein in normal and tumor tissue using the generated antibodies showed that the UBE1L protein was present in normal lung cells and non-lung cancer cell lines, but was undetectable in all 14 human lung cancer cell lines analyzed. This difference in expression of the UBE1L protein between normal lung tissue and lung tumor-derived cell lines suggests a possible involvement of an E1-like protein in the origin and/or progression of lung tumors.