An Analysis of Nucleotide Polymorphism in the Human MT-IIa Gene Promoter Region

Abstract

Previous research has shown varying degrees of renal damage on exposure to equal amounts of cadmium in occupationally exposed mining and factory workers. Further work has shown that in vitro exposure of human peripheral lymphocytes to the same cadmium levels resulted in significant variation in Metallothionein (MT) mRNA transcriptional induction over basal MT mRNA expression in a series of individuals. This variation could account for the differences in renal Cd toxicities identified previously. In this study, the human MT-IIₐ gene was cloned from 12 individuals, and the 5'promoter region was sequenced for each to determine the extent of promoter nucleotide variation. This is of interest since such an analysis has not been done in the past. No study has been done to look at the degree of polymorphism in a particular promoter region. Thus, there are no data on the degree of nucleotide drift or change which can occur in promoter regulatory elements. Such a study could provide insight into whether promoter changes could result in the type of variation described above. It could also give some insight into the degree of variation in sequences in the literature. The results obtained indicated that the human MT-IIₐ promoter region is highly conserved, with only one polymorphic site identified at position 557, between the glucocorticoid responsive element and the fourth metal regulatory element sequences. This suggests that promoter variation is not likely a significant yfactor in MT mRNA induction variability, although further analysis would be needed to show this since only 12 people were analyzed. The results were compared against a study of nucleotide polymorphism in Drosophila melanogaster, which is the only other data on nucleotide variation specifically (Kreitman, 1983; Kreitman and Hudson, 1991). As well, a number of discrepancies were noted from the original published sequences in the literature, suggesting that errors are likely published in genomic sequence which are never identified, except through trial and error. This has potential repercussions when considering the use of such sequence in cloning and sequencing projects, like the sequencing of the human genome, since this would depend on the accuracy of previously published data.