Human cytoplasmic superoxide dismutase cDNA clone: a probe for studying the molecular biology of Down syndrome.

The gene locus for human cytoplasmic superoxide dismutase (SOD-1; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is located in or near a region of chromosome 21 known to be involved in Down syndrome. To approach the molecular biology of this genetic disease we have constructed a SOD-1 cDNA clone. Poly(A)-containing RNA enriched for human SOD-1 mRNA was isolated, used to synthesize double-stranded cDNA, and inserted into the endonuclease Pst I site of the plasmid pBR322. The chimeric molecules were used to transform Escherichia coli. Two clones containing SOD-1 cDNA inserts were identified by their ability to hybridize specifically with mRNA coding for SOD-1. Each of these clones carries a 650-base-pair insert, as was determined by restriction enzyme digestion and electron microscopic heteroduplex analysis. Hybridization of labeled cloned cDNA to RNA blots revealed two distinct SOD-1 mRNA classes of 500 and 700 nucleotides. The data suggest that both are polyadenylylated and are coded by chromosome 21.