Evidence that glutathione peroxidase RNA and manganese superoxide dismutase RNA bind the same protein

Rat lung extract contains protein that binds to a cis element in the 3' untranslated region of glutathione peroxidase (GPx) mRNA; this region is located 200 bases downstream of the stop codon and 77 bases downstream of the selenocysteine insertion sequence. GPx mRNA-binding protein (GPx-BP) has the following characteristics in common with Mn superoxide dismutase mRNA-binding protein (MnSOD-BP): 1. RNA-binding activity is redox-sensitive; free sulfhydryl groups on the protein are required for binding. 2. RNA-binding activity is enriched in a 130,000 x g supernatant fraction and is inhibited by RNA in the polysomal fraction. 3. The MnSOD and GPx cis elements compete with each other for protein binding. 4. UV crosslinking studies with each probe reveal a [32P]-labeled protein of the same apparent molecular mass, 56 kDa. These observations provide evidence that MnSOD and GPx RNAs bind the same protein.