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The structure and gene expression of a number of metallothionein (MT) genes of the sea urchin Lytechinus pictus were characterized. The MT genes in this species are members of a small gene family composed of 7 to 10 copies per haploid genome. A genomic library was constructed and 81 clones containing MT sequences were isolated of which 8 were analyzed. The complete sequence of one clone (LpMT1) and the promoter region of 7 others was determined. LpMT1 encodes a primary transcript of 3042 bp composed of 4 exons which is processed into a mRNA of 605 bases. The promoter regions of all the genes analyzed are highly conserved and contain multiple copies of the metal responsive enhancer element consensus sequence. L. pictus eggs injected with MT promoter fused to a CAT reporter gene, and cultured to various stages of development, directed transcription in a metal inducible fashion. The promoters also direct transcription in the sea urchin Strongylocentrotus purpuratus and in a human HeLa cell line. Deletion analysis indicates that the LpMT1 promoter requires regulatory elements other than the two metal responsive elements.