A guanosine quadruplex and two stable hairpins flank a major cleavage site in insulin-like growth factor II mRNA

Abstract

Insulin-like growth factor II (IGF-II) mRNAs are cleaved by an endonucleolytlc event in a conserved part of their 3' untranslated region that is predicted to exhibit a complex higher-order RNA structure. In the present study, we have examined the putative secondary structures of In vitro transcripts from the conserved part of human and rat mRNAs by enzymatic and chemical probing. The results show that the cleavage site Is situated between two highly structured domains. The upstream domain consists of two large hairpins, whereas the downstream domain Is guanoslne-rlch. The guanoslne-rich domain adopts a compact unimolecular conformation in Na+ or K+ but not in Li +, and It completely arrests reverse transcription in K+ but only partially in Na +, Indicating the presence of an intramolecular guanosine quadruplex. The flanking higher-order structures may ensure that the cleavage site is not sequestered In stable RNA structures, thus allowing interactions with RNA or proteins at posttranscrlptlonal stages of IGF-II expression. © 1994 Oxford University Press.