DEFINING A NOVEL CIS-ELEMENT IN THE 3'-UNTRANSLATED REGION OF MAMMALIAN RIBONUCLEOTIDE REDUCTASE COMPONENT R2 MESSENGER-RNA - CIS-TRANS-INTERACTIONS AND MESSAGE STABILITY

Mammalian ribonucleotide reductase is a highly regulated activity esse ntial for DNA synthesis and repair. The 3'-untranslated region (3'-UTR ) of mammalian ribonucleotide reductase R2 mRNA has been implicated in the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate-mediated sta bilization of mouse BALB/c 3T3 R2 message. We investigated the possibi lity that the 3'-UTR contains regulatory information for R2 mRNA turno ver. Using 3'-end-labeled RNA in gel shift and UV cross-linking analys es, we detected in the 3'-UTR a novel 9-nucleotide cis-element, 5'UCGU GUGCU-3', which interacted with a widely distributed cellular cytosoli c protease-sensitive factor(s) in a sequence-specific manner to form a 45-kDa R2 binding protein complex. The binding activity was redox-sen sitive and down-regulated by 12-O-tetradecanoylphorbol-13-acetate and okadaic acid in a dose-dependent manner. Insertion of a 154-base pair fragment containing the cis-element led to markedly reduced accumulati on of chloramphenicol acetyltransferase hybrid mRNA relative to the sa me insert carrying a series of G --> A mutations within this element t hat eliminated binding. We suggest that the 9-nucleotide region functi ons as a destabilizing element. These results provide a model for ribo nucleotide reductase gene expression through a novel and specific mRNA cis-trans-interaction involving a phosphorylation signal pathway that leads to changes in the stability of R2 message.