Genomic clones containing the human pyruvate kinase M (PKM) gene, which encodes the M1-type and M2-type isozymes, were isolated and their exon sequences were determined. The gene is approximately 32 kb and consists of 12 exons and 11 introns. Exons 9 and 10 contain sequences specific to the M1 and M2 types, respectively, indicating that the human isozymes are produced from the same gene by alternative splicing as in the case of the rat gene. The exon-intron structure of the human PKM gene is identical to that of the rat gene, and the introns of both genes interrupt the exons at the same points. Introns 6 and 7 begin with GC dinucleotide instead of the consensus GT, but the other exon-intron boundaries are consistent with the GT-AG rule. The gene is transcribed from multiple start sites. The 5'-flanking region of the gene contains putative Sp1-binding sites, but no TATA box or CAAT box, and shows high sequence similarity to that of the rat M gene. Bacterial chloramphenicol acetyltransferase assay revealed that the upstream region between positions -493 and -51 contained a cis-acting element(s) that was essential for expression of the M gene in HeLa cells. Long stretches of conserved regions were found in the introns around the M1-specific and M2-specific exons, suggesting that these regions may be involved in the alternative splicing machinery.