CLONING, EXPRESSION, AND CHARACTERIZATION OF 2 MANGANESE SUPEROXIDE DISMUTASES FROM CAENORHABDITIS-ELEGANS

Two genes encoding manganese superoxide dismutase (sod-2 and sod-3) ha ve been identified in the nematode Caenorhabditis elegans. Each gene i s composed of five exons, and intron positions are identical; however, intron sizes and sequences are not the same, The predicted protein se quences are 86.3% homologous (91.8% conservative), and the cDNAs are o nly 75.2% homologous, Both deduced protein sequences contain the expec ted N-terminal mitochondrial transit peptides. Reverse transcriptase p olymerase chain reaction analysis shows that both genes are expressed under normal growth conditions and that their RNA transcripts are tran s-spliced to the SL-1 leader sequence. The latter result together with Northern blot analysis indicate that both genes have mono-cistronic t ranscripts, The sod-3 gene was mapped to chromosome X, and the locatio n of sod-2 was confirmed to be chromosome I, Polymerase chain reaction was used to amplify the cDNA regions encoding the predicted mature ma nganese superoxide dismutase proteins and each was cloned and expresse d to high levels in Escherichia coli cells deficient in cytosolic supe roxide dismutases. Both proteins were shown to be active in E. coli, p roviding similar protection against methyl viologen-induced oxidative stress. The expressed enzymes, which were not inhibited by hydrogen pe roxide or cyanide, are dimeric, show quite different electrophoretic m obilities and isoelectric points, but exhibit comparable specific acti vities.