THE PLANT CELL, Vol 6, Issue 1 135-145, Copyright © 1994 by American Society of Plant Biologists
Binding of a 50-kD Protein to a U-Rich Sequence in an mRNA Encoding a Proline-Rich Protein That Is Destabilized by Fungal Elicitor
S. Zhang and M. C. Mehdy
Department of Botany, University of Texas, Austin, Texas 78713
The mRNA encoding the bean proline-rich protein PvPRP1 has been shown
previously to be destabilized in elicitor-treated cells. In this study, we
identified a 50-kD protein in cellular extracts that binds specifically to
the PvPRP1 mRNA by UV cross-linking assays. Using 32P-labeled RNAs
transcribed in vitro from a series of 5[prime] deleted PvPRP1 cDNA clones,
we demonstrated that the PvPRP1 mRNA binding protein (PRP-BP) binds to a
27-nucleotide U-rich (~60%) domain in the 3[prime] untranslated region.
Poly(U) and, to a lesser extent, poly(A-U) competed for the PRP-BP binding
activity. PRP-BP activity is redox regulated in vitro, as shown by the
effects of sulfhydryl-modifying reagents on the RNA binding activity.
Treatment of cellular extracts with the reducing agents DTT and
[beta]-mercaptoethanol increased binding activity, whereas treatment with
the oxidizing agent diamide and the alkylating agent N-ethylmaleimide
inhibited binding. In extracts from elicitor-treated cells, PRP-BP activity
increased approximately fivefold prior to rapid PvPRP1 mRNA degradation.
The increase in PRP-BP activity was apparently due to post-translational
regulation because control and elicitor-treated cell extracts supplemented
with DTT showed high comparable levels of RNA binding activity. The
kinetics of PRP-BP activation after elicitor treatment and its capacity for
redox regulation in vitro suggested that PRP-BP may function in the
elicitor-induced destabilization of PvPRP1 mRNA.
