RNA IN POLYSOMES IS AN INHIBITOR OF MANGANESE SUPEROXIDE-DISMUTASE RNA-BINDING PROTEIN-ACTIVITY

A redox-sensitive protein in rat lung binds to the 3'-untranslated reg ion (3'-UTR) of manganese superoxide dismutase (Mn-SOD) mRNA; the acti vity of this Mn-SOD RNA-binding protein (Mn-SOD-BP) is greater in 12,0 00-g supernatant fractions (S12) from neonates than in S12 from adults (H. Fazzone, A. Wangner, and L. B. Clerch. J. Clin. Invest. 92: 1278- 1281, 1993). To determine the mechanism underlying this developmental difference, lung subcellular fractions were tested for their effect on Mn-SOD-BP activity. Protein in the 130,000-g supernatant (S130) of lu ng extracts bound the 3'-UTR. However, the developmental difference in binding was not present in S130. The 130,000-g pellet (P130) did not bind the 3'-UTR; rather, it contained an inhibitor of Mn-SOD-BP activi ty. Addition of P130 to S130 decreased RNA binding in a dose-dependent manner. Furthermore, adult P130 was a more potent inhibitor of RNA-bi nding activity than neonatal P130. These data indicate that the develo pmental difference in Mn-SOD-BP activity is due, in part, to an inhibi tor in P130. Biochemical characterization revealed that the inhibitor is an RNA that may participate in the posttranscriptional control of M n-SOD gene expression.