ANALYSIS OF REGULATORY ELEMENTS FLANKING METALLOTHIONEIN GENES IN CD-TOLERANT FISH (PIKE AND STONE LOACH)

From genomic libraries constructed for both pike and stone loach, clon es were isolated containing the metallothionein genes from these two s pecies of cadmium-tolerant fish. A single copy metallothionein gene wa s identified in each species by Southern blot analysis. Sequencing rev ealed that each gene consisted of three exons followed by polyadenylat ion signals at the 3' end. In the 5' flanking region, putative metal r esponsive elements were identified both close to the transcription sta rt site and clustered distally approx. 500 bp upstream. Neither gene l ocus showed any homology with the glucocorticoid or interferon respons ive elements that have been identified in mammalian species. The signi ficance of the absence of such responsive elements and their replaceme nt by additional metal responsive elements in the same location of the 5'-flanking region of the MT genes is discussed in relation to the or ganisation of the MT gene loci in (the Cd-sensitive) rainbow trout and higher mammalian species.