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 act ive site for complex and dynamic interactions involving RNA-binding protein s. The spatial, temporal, and phylogenetic distribution of the Cas-1 3'-UTR U-rich motif-specific RNA-binding proteins was evaluated by gel mobility s hift and UV cross-linking assays. The specific RNA-protein complexes were o bserved in mouse tissue homogenates representing developmental stages as ea rly as day 10 pc and ranged in molecular weight from similar to 38 kDa to s imilar to 52 kDa. These mRNA-protein complexes appeared in all vertebrate s pecies examined (human, mouse, rat, dog, rabbit, chicken, fish, and frog) b ut not in insects. The similar to 38-kDa protein was the most prominent pro tein in vertebrates. The cDNA sequence of the mouse similar to 38-kDa prote in was obtained by purification of the protein, microsequencing, and RT-PCR . The resulting 456-nt sequence, representing the partial internal cDNA seq uence, and its deduced amino acid sequence were similar to the RNA recognit ion 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.