Total RNA from human reticulocytes was purified and reverse-transcribed into cDNA using an oligo-dT primer. This cDNA was used as a template for a polymerase chain reaction (PCR) with a primer specific for the N-terminal sequence of mammalian metallothioneins (MT) and a universal primer. A single amplified fragment was thus generated which when cloned and sequenced revealed two distinct MT cDNAs of almost identical molecular weights. One sequence was identical to that previously reported for human MT II and the other encoded a novel MT I isoform (MT IR). The DNA sequence of MT 1R is distinct from those documented for other MT I isoforms.
