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 re ticulum (ER) system in developing rice endosperm. Instead they are localize d on the surface of the prolamine protein bodies (PBs). Recent findings sug gest 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 wit h this organelle. To uncover the molecular and cellular basis for the local ization of prolamine mRNAs in the rice endosperm cells, we obtained a enric hed cytoskeleton-PB fraction and studied the RNA binding activities associa ted from fractions obtained from poly(U)-Sepharose. Using a RNA-protein UV cross-linking assay we identified a dominant 40-kDa RNA-binding protein ass ociated with the cytoskeleton-PB-enriched fraction. This activity binds to the 3' and 5' untranslated regions of prolamine mRNA and the 3' untranslate d region of glutelin mRNA but not to their coding sequences. Binding activi ty is readily competed by polyadenylic acid indicating that the binding rec ognition site is A-rich. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.