Transglutaminase 1 (TG1) is an enzyme that is expressed and activated during terminal differentiation of keratinocytes and synthesizes cornified envelope by a cross-linking reaction. The gene encoding human TG1 was isolated from human genomic DNA and characterized. It spans 14.3 kilobase pairs and is composed of 15 exons. All exon-intron junctional sequences conformed to the canonical GT-AG rule. The translation start was located in the second exon. The active site Cys residue of the enzyme was in exon 7. The coding sequence for human TG1 was comprised of 2454 nucleotides identical with the published human TG1-cDNA sequence (Yamanishi, K., Liew, F.-M., Konishi, K., Yasuno, H., Doi, H., Hirano, J., and Fukushima, S. (1991) Biochem. Biophys. Res. Commun. 175, 906-913). The sizes of exons from 3 to 14 were markedly conserved between the genes for the human TG1 and factor XIIIa, another member of the transglutaminase family. The one major and two minor transcription initiation sites of the TG1 gene were determined by primer extension. The 5'-flanking region of the human TG1 gene showed features of a housekeeping gene and contained potential regulatory motifs, including elements found in keratinocyte-related genes. The chromosome sublocalization of the TG1 gene was assigned to 14q11.2.