Onchocerca volvulus superoxide dismutase genes: Identification of functional promoters for pre-mRNA transcripts which undergo trans-splicing

Onchocerca volvulus superoxide dismutase genes: Identification of functiona l promoters for pre-mRNA transcripts which undergo trans-splicing. Experime ntal Parasitology 94, 172-179. The genes encoding three forms of superoxide dismutase. the cytosolic and extracellular CuZn superoxide dismutases and the mitochondrial Mn superoxide dismutase, were isolated from an Onchocerca volvulus lambda fix II genomic library. Genomic Southern blot analyses ind icate single-copy genes in the O. volvulus genome. The O. volvulus cytosoli c and extracellular CuZnSQD genes (Ov-sod-1 and Ov-sod-2) are separated by 0.8 kb of sequence and are convergently transcribed. Since the transcripts from all three sod genes are trans-spliced. the transcription start point o f each gene was determined in a heterologous system that lacks trans-splici ng machinery by in vitro transcription using Drosophila embryo nuclear extr acts, followed by primer extension experiments. The ability of the 5' flank ing region of the genes encoding the three Ov-SODs to promote transcription was further examined in transient transfections of Chinese hamster ovary c ells. In firefly luciferase reporter assays, the Ov-sod-1 and -2 and the Mn SOD (Ov-sod-3) gene promoters showed minimal. strong, and moderate levels o r activity in these cells, respectively. Both Ov-sod-2 and -3 gene promoter regions showed an initial increase in activity in response to 5' deletions . The results from the in vitro transcription experiments and the luciferas e reporter assays were consistent and suggest the presence of Inr-like elem ents in the promoter regions of the Ov-sod genes. (C) 2000 Academic Press.