CLEAVAGE PROPERTIES OF AN ESTROGEN-REGULATED POLYSOMAL RIBONUCLEASE INVOLVED IN THE DESTABILIZATION OF ALBUMIN MESSENGER-RNA

Previous work from this laboratory [Dompenciel, R.E., Garnepudi, V.R. and Schoenberg, D.R. (1995) J. Biol. Chem. 270, 610-6118] described th e purification and properties of an estrogen-regulated endonuclease is olated from Xenopus liver polysomes that is involved in the destabiliz ation of albumin mRNA. The present study mapped cleavages made by this enzyme onto the secondary structure of the portion of albumin mRNA be aring the major cleavage sites, The predominant cleavages occur in the overlapping APyrUGA sequence AUUGACUGA present in a single-stranded l oop region, and in AUUGA located within a bulged AU-rich stem, A struc tural mutation which converted the major loop cleavage site to a hairp in bearing one APyrUGA element eliminated cleavage at the intact site. This confirms that the polysomal RNase is specific for single-strande d RNA. Additional point mutations in the major loop characterized the nucleoside sequence requirements for cleavage, Finally, snake venom ex onuclease was used to demonstrate the polysomal RNase generates produc ts with a 3' hydroxyl. Binding of an estrogen-induced protein to a por tion of the 3' UTR of vitellogenin mRNA may be involved in its stabili zation by estrogen [Dodson, R.E. and Shapiro, D.J. (1994) Mel. Cell. B iol. 14, 3130-3138]. The core binding;site for this protein bears the sequence APyrUGA, suggesting that stabilization maybe accomplished by occlusion of a cleavage site for the polysomal RNase.