METALLOTHIONEIN GENE-EXPRESSION IN EMBRYOS OF THE SEA-URCHIN LYTECHINUS-PICTUS

The metallothionein (MT) gene LpMT1 of the sea urchin Lytechinus pictu s was characterized. The primary transcript of 3042 nucleotides includ es four exons, as uniquely observed for other sea urchin MT genes, whi ch are spliced to form a messenger RNA of 605 nucleotides. The deduced LpMT1 protein sequence includes 69 amino acids, move than observed fo r other MT proteins, For a high level of inducible activity, the LpMT1 promoter requires sequence elements in addition to the canonical regu latory elements identified for mammalian MT promoters. The promoter of the closely related LpMT2 gene is very active in spite of its lack of a distinctive poly(C) element included in a sequence tract required f or fully induced activity of the LpMT1 promoter. In contrast to embryo s of the sea urchin S. purpuratus in which MT mRNAs are restricted to the aboral ectoderm of uninduced embryos, no spatially preferential ac cumulation of MT mRNAs in L. pictus embryos was observed. The cis-acti ng regulatory elements required for MT gene activity and the spatial s pecificity of MT gene expression in sea urchin embryos are considered. The LpMT1 and LpMT2 promoters constitute promiscous promoters that ca n be induced to a high level of activity. (C) 1997 Wiley-Liss, Inc.