Lysyl oxidase (EC 22.214.171.124), an extracellular copper enzyme, initiates the crosslinking of collagens and elastin by catalyzing oxidative deamination of the epsilon-amino group in certain lysine and hydroxylysine residues. We report here that the human lysyl oxidase gene is about 15 kb in size and consists of seven exons. Transcription is initiated at one major site and four minor sites, and the first exon consists of 273 bp of untranslated sequences (calculated to the major site) and 631 bp of translated sequences, which accounts for about half of all the translated sequences of the gene. The seventh exon, on the other hand, codes for only the last codon of amino acid 416 and for amino acid 417, which are followed by the translation termination codon and the 3' untranslated sequences. Exons 2-6 vary in size from 96 to 157 bp, and the introns from 331 bp to about 3.5 kb. The 5' flanking region contains a TATA-like sequence at -30 relative to the major transcription initiation site and a CCAAT motif at -109. The 5' flanking region and the downstream sequences present in the first exon and first intron contain altogether five possible binding sequences for Sp1, six for AP-2, one for AP-1, three for PEA3, three for MEP-1, and three CCCTCCC motifs, all of which may be involved in the regulation of the expression of the gene.