We have cloned and characterized a novel gene at the site of a t(1;3)(p34;p21) translocation breakpoint in T-cell acute lymphoblastic leukemia. A cDNA for this gene, for which we propose the designation TCTA (T-cell leukemia translocation-associated gene), has been cloned. TCTA mRNA is expressed ubiquitously in normal tissues, with the highest levels of expression seen in the kidney. The TCTA gene is conserved throughout evolution in organisms ranging from Drosophila to humans. A short open reading frame encodes a predicted M(r) 12,000 protein without strong homology to any previously reported proteins. Of note, genomic Southern blots demonstrated a reduced TCTA signal in three of four small cell lung cancer cell lines tested, suggesting loss of one of the two copies of the gene.