EVOLUTIONARY CONSERVATION OF THE AU-RICH 3' UNTRANSLATED REGION OF MESSENGER-RNA

AU-rich sequence motifs (specifically sequences containing reiteration s of AUUUA) are found in the 3' untranslated region of mammalian mRNAs encoding cytokines, adhesion molecules, and protooncogenes. Because t hese AU-rich elements (3'AURE) have been observed to reduce the stabil ity and translational efficiency of transcripts that contain them, and because many of these transcripts accumulate in cells exposed to infl ammatory stimuli, we reasoned that mRNAs with 3'AURE may be highly con served and that the AURE is a marker of mRNAs that are inducible by en vironmental stressors. To test this hypothesis, we developed a polymer ase chain reaction (PCR) strategy to isolate specifically mRNAs with 3 'AURE. We first validated the effectiveness of this approach by select ively amplifying two mRNAs containing 3'AURE from interleukin 1 (IL-1) -induced human endothelial cells, then used the same primers in revers e transcriptase-PCR of sea urchin RNA, and used the radiolabelled reac tion products to screen a cDNA library prepared from endotoxin-exposed sea urchin coelomocytes. We identified 124 positive clones and isolat ed a 1608-base-pair fragment that contains an AU-rich consensus sequen ce upstream from a poly(A) tail. This sea urchin transcript hybridizes with immobilized poly(A)(+)- selected RNA prepared from living coelom ocytes maintained in vitro for 8.5-13 h but not with RNA prepared from freshly harvested coelomocytes. Our results provide support for the g rowing body of evidence that 3'AURE are both conserved and functional and indicate further that isolation and short-term in vitro culture of sea urchin coelomocytes is sufficient to induce the expression of tra nscripts containing 3'AURE.