title: Effects of heavy metals on Drosophila larvae and a metallothionein cDNA.
abstract: Drosophila melanogaster larvae reared on food containing radioactive cadmium retained over 80% of it, mostly in the intestinal epithelium. The majority of this radioactivity was associated with a soluble protein of less than 10,000 molecular weight. Synthesis of this cadmium-binding protein was induced by the metal as demonstrated by incorporation of radioactive cysteine. Most copper ingested by larvae was also found to associate with a low molecular weight, inducible protein, but some of it was found in an insoluble fraction. Zinc was unable to, or very inefficient at, binding or inducing the synthesis of a similar protein. A D. melanogaster cDNA clone was isolated based on its more intense hybridization to copies of RNA sequences from copper-fed larvae than from control larvae. This clone showed strong hybridization to mouse metallothionein-I cDNA at reduced stringency. Its nucleotide sequence includes an open-reading segment which codes for a 40-amino acid protein; this protein was identified as metallothionein based on its similarity to the amino-terminal portion of mammalian and crab metalloproteins. The ten cysteine residues present occur in five pairs of near-vicinal cysteines (Cys-X-Cys). This cDNA sequence hybridized to a 400-nucleotide polyadenylated RNA whose presence in the cells of the alimentary canal of larvae was stimulated by ingestion of cadmium or copper; in other tissues this RNA was present at much lower levels. Mercury, silver, and zinc induced metallothionein to a lesser extent. Whether (any of) the protein(s) discussed above correspond(s) to that coded by this RNA sequence has not yet been determined.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002104:Cadmium / Q000378:metabolism* / Q000633:toxicity; D003001:Cloning, Molecular; D003300:Copper / Q000633:toxicity; D003545:Cysteine / Q000378:metabolism; D004247:DNA / Q000235:genetics; D004331:Drosophila melanogaster / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D007814:Larva / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism / Q000648:ultrastructure; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism*; D012834:Silver / Q000633:toxicity; D015032:Zinc / Q000633:toxicity
chemical_list: D002104:Cadmium; D012834:Silver; D003300:Copper; D004247:DNA; D008668:Metallothionein; D015032:Zinc; D003545:Cysteine