Distribution and Molecular Characterization of mRNA-Binding Proteins Specific to the (U) 15 Region of 3′ UTR of the Mouse Catalase ( Cas-1 )

The 3′ UTR of the mouse Cas-1 mRNA, encoding the antioxidant enzyme catalase, has a U-rich motif that is conserved across species. This motif is an active site for complex and dynamic interactions involving RNA-binding proteins. The spatial, temporal, and phylogenetic distribution of the Cas-1 3′-UTR U-rich motif-specific RNA-binding proteins was evaluated by gel mobility shift and UV cross-linking assays. The specific RNA-protein complexes were observed in mouse tissue homogenates representing developmental stages as early as day 10 pc and ranged in molecular weight from ∼38 kDa to∼52 kDa. These mRNA-protein complexes appeared in all vertebrate species examined (human, mouse, rat, dog, rabbit, chicken, fish, and frog) but not in insects. The ∼38-kDa protein was the most prominent protein in vertebrates. The cDNA sequence of the mouse ∼38-kDa protein was obtained by purification of the protein, microsequencing, and RT-PCR. The resulting 456-nt sequence, representing the partial internal cDNA sequence, and its deduced amino acid sequence were similar to the RNA recognition motif (RRM) of a protein superfamily, implicated in splicing, stability, localization, and translation of RNAs. Although the results suggest that cis element-binding activity could be a cytoplasmic regulator of Cas-1 mRNA metabolism, the significance of this binding remains to be determined.