A cytoskeleton-associated RNA-binding protein binds to the untranslated regions of prolamine mRNA and to poly(A)

Prolamine mRNAs are not randomly translated on the extensive endoplasmic reticulum (ER) system in developing rice endosperm. Instead they are localized on the surface of the prolamine protein bodies (PBs). Recent findings suggest that prolamine polysomes are attached to the surface of the prolamine PBs not only to the ER but also to the cytoskeleton which is associated with this organelle. To uncover the molecular and cellular basis for the localization of prolamine mRNAs in the rice endosperm cells, we obtained a enriched cytoskeleton-PB fraction and studied the RNA binding activities associated from fractions obtained from poly(U)-Sepharose. Using a RNA-protein UV cross-linking assay we identified a dominant 40-kDa RNA-binding protein associated with the cytoskeleton-PB-enriched fraction. This activity binds to the 3' and 5' untranslated regions of prolamine mRNA and the 3' untranslated region of glutelin mRNA but not to their coding sequences. Binding activity is readily competed by polyadenylic acid indicating that the binding recognition site is A-rich. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.