Human metallothionein MT-I and MT-II processed genes.

Two intronless pseudogenes, corresponding to the human metallothionein MT-I and MT-II processed genes, have been isolated from a human genomic library. MT-I processed gene has accumulated a number of mutations including a nonsense mutation giving rise to a termination codon at amino acid position 21, and a single base deletion at amino acid position 47 causing a shift in the reading frame. MT-II processed gene is a full-length perfect copy of its corresponding mRNA except for a few mutations. Most of the mutations in MT-II processed gene are silent except that the amino acid glycine (GGT) at position 10 is changed to serine (AGT) due to a transition. Both MT-I and MT-II processed genes possess poly(A) sequences of 21 and 17 nucleotides, respectively, 3' to the consensus AATAAA sequence. While these genes are quite similar in their sequences at the 3'-untranslated region, they show less than 50% homology in the 5'-untranslated sequences. Two direct repeats of 16 and 18 nucleotides in length define the limits of the MT-I and MT-II processed genes, respectively, and have been confirmed by S1 nuclease mapping analysis. In both MT-I and MT-II processed genes these direct repeats towards the 5' end of the gene start with an AhaIII (TTTAAA) restriction site. Our studies suggest that these direct repeats are the results of the insertion site duplication.