Metallothioneins (MTs) are short, cysteine-rich proteins for heavy metal homeostasis and detoxification; they bind a variety of heavy metals and also act as radical scavengers. Transcription of mammalian MT genes is activated by heavy metal load via the metal-responsive transcription factor 1 (MTF-1), an essential zinc finger protein whose elimination in… (More)
FIG. 5. Drosophila MRE-like motifs can confer heavy metal response. The promoter of the embryonic MT gene (Mto) of Drosophila contains four MRE-like motifs (51), which, however, were found by EMSA to bind relatively poorly to MTF-1 under our standard experimental conditions. (A) To evaluate their potential, a minipromoter was assembled into a OVEC reporter construct as shown (for details, see Materials and Methods) and was transfected into S2 cells with or without a dMTF-1 expression vector. a to d indicate four MRE-like sequence motifs. Numbering refers to nucleotide position relative to transcription start. (B) Cytoplasmic RNA was isolated after metal induction for 24 h, and 160 mg of the RNA was subjected to nuclease S1 mapping as shown. Zn21 induction, 100 mM ZnCl2; Cd 21 induction, 20 mM CdCl2; Cu 21 induction, 500 mM CuSO4; F, free S1 oligonucleotide probe; S, correctly initiated reporter gene transcripts.2, absence of dMTF-1.