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Gustavo Maroni, Ann-Shu Ho, and Laurent Theodore

Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280 USA

Abstract
Flies from a transgenic line of Drosophila melanogaster with two copies of the metallothionein allele Mtn^.3 were more tolerant to cadmium than strains with only one copy of the gene. However, flies with the Mtn ^.3 allele were as tolerant as flies with the Mtn ¹ allele, despite the level of expression of Mtn ¹ being three times higher than that of Mtn ^.3. We propose that the substitution of Lys-40 (in Mtn ^.3) for Glu-40 (in Mtn ¹) accounts for a reduction in binding affinity of Mtn¹, which offsets the increased expression levels. Key words: cadmium tolerance, Drosophila melanogaster, gene duplication, life span, metallothionein, Mtn gene, viability. Environ Health Perspect 103:1116-1118 (1995)

Address correspondence to G. Maroni, Department of Biology, CB 3280, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280 USA.

L. Theodore is currently at the Laboratoire d'Embriologie Moléculaire et Expérimentale, Université de Paris XI, 91405 Orsay Cedex, France. We are grateful to Donna Maroni for helpful editorial comments. This research was supported with a grant from the National Institute of Environmental Health Sciences PHS ES02654.

Received 6 July 1995 ; accepted 11 August 1995.