A 3′-Untranslated Region of Catalase Messenger-RNA Composed of a Stem-Loop and Dinucleotide Repeat Elements Binds a 69-kDa Redox-Sensitive Protein

Rat lung extract contains protein that forms redox-sensitive, specific complexes with a 1130-base catalase cRNA (J. Biol. Chem. 267, 2853-2855, 1992). The present paper reports studies aimed at delimiting the site of protein binding on the RNA and characterizing the protein. A 240-base sequence was identified as the 3′ untranslated region of catalase mRNA that binds lung protein in a redox-sensitive manner. Two elements within this 240-base region bind protein; one is a 36-base element that has a computer-predicted stem-loop secondary structure and the other is a CA dinucleotide repeat. Competition studies indicate that both elements are required for specific binding. Cross-competition experiments demonstrated that catalase RNA-binding protein (CAT-BP) is not the iron-responsive element-binding protein. Ultraviolet light-induced cross-linking and two-dimensional electrophoresis showed that CAT-BP has an apparent molecular mass of 69 kDa and appears to be composed of four isoforms. Competition studies indicate the stem-loop cis element is directly involved in binding CAT-BP. In addition to rat, the 69-kDa catalase RNA-binding protein is present in mouse and human fibroblast cell lines.