cDNa cloning and nucleotide sequence comparison of Chinese hamster metallothionein I and II mRNAs

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Abstract
Polyadenylated RNA was extracted from a cadmium resistant Chinese hamster (CHO) cell line, enriohed for metal-induced, abundant RNA sequences and cloned as double-stranded cENA in the pi asm id pBR322. Two cDNA clones, pCHMTI and pCHHT2, encoding two Chinese hamster isometallothioneins were identified, and the nucleotide sequence of each insert was determined. The two Chinese hamster metallothioneins show nucleotide sequence homologies of 80% in the protein coding region and approximately 35% in both the 5‘ and 3’ untranslated regions. Interestingly, an 8 nucleotide sequence (TGTAAATA) has been conserved in sequence and position in the 3‘ untranslated regions of each metallothionein mRNA sequenced thus far. Estimated nucleotide substitution rates derived from interspecies comparisons were used to calculate a metallothionein gene duplication time of 45 to 120 million years ago.