A gender-specific mRNA encoding a cytotoxic ribonuclease contains a 3 ' UTR of unusual length and structure

A cDNA (2855 nt) encoding a putative cytotoxic ribonuclease (rapLR1) relate d to the antitumor protein onconase was cloned from a library derived from the liver of gravid female amphibian Rana pipiens. The cDNA was mainly comp rised (83%) of 3' untranslated region (UTR). Secondary structure analysis p redicted two unusual folding regions (UFRs) in the RNA 3' UTR. Two of these regions (711-1442 and 1877-2130 nt) contained remarkable, stalk-like, stem -loop structures greater than 38 and 12 standard deviations more stable tha n by chance, respectively, Secondary structure modeling demonstrated simila r structures in the 3' UTRs of other species at low frequencies (0.01-0.3%) . The size of the rapLR1 cDNA corresponded to the major hybridizing RNA cro ss-reactive with a genomic clone encoding onconase (3.6 kb). The transcript was found only in liver mRNA from female frogs. In contrast, immunoreactiv e onconase protein was detected only in oocytes. Deletion of the 3' UTR fac ilitated the in vitro translation of the rapLR1 cDNA. Taken together these results suggest that these unusual UFRs may affect mRNA metabolism and/or t ranslation.