RNA-RNA INTERACTION IS REQUIRED FOR THE FORMATION OF SPECIFIC BICOID MESSENGER-RNA 3' UTR-STAUFEN RIBONUCLEOPROTEIN-PARTICLES

The formation of the anterior pattern of the Drosophila embryo is depe ndent on the localization of the mRNA of the morphogen Bicoid (bcd) to the anterior pole of the egg cell, Staufen protein (ST;IU) is require d in a late step of the localization to anchor the bcd mRNA in the ant erior cytoplasm, We have shown previously that endogenous STAU associa tes specifically with injected bcd mRNA 3'-untranslated region (UTR), resulting in the formation of characteristic RNA-protein particles tha t are transported along microtubules of the mitotic spindles ina direc ted manner. The regions recognized by STAU in this in vivo assay are p redicted to form three stem-loop structures involving large double-str anded stretches, Here, we show that the STAU interaction requires a do uble-stranded conformation of the stems within the RNA localization si gnal, In addition, base pairing between two single-stranded loops play s a major role in particle formation, This loop-loop interaction is in termolecular, not intramolecular; thus dimers or multimers of the RNA localization signal must be associated with STAU in these particles, T he bcd mRNA 3' UTR can also dimerize in vitro in the absence of STAU. Thus, in addition to RNA-protein interactions, RNA-RNA interaction mig ht be involved in the formation of ribonucleoprotein particles for tra nsport and localization.