Isolation and characterization of the 102-kilodalton RNA-binding protein that binds to the 5' and 3' translational enhancers of tobacco mosaic virus RNA.

Tobacco mosaic virus (TMV) is a positive-sense, single-stranded RNA virus the genome of which acts as a mRNA in the cytoplasm. On infection, TMV mRNA is efficiently and selectively translated by the host translation machinery despite the lack of a poly(A) tail, which is normally required for efficient translation. Both the 68-base 5' leader (Omega) and the 205-base 3' untranslated region of TMV promote efficient translation. A 25-base poly(CAA) region within Omega and the upstream pseudoknot domain, a 72-base region composed of three RNA pseudoknots, are responsible for the translational regulation. We have identified, purified, and characterized a 102-kDa RNA-binding protein (p102) from wheat that binds specifically to the poly(CAA) region within Omega and the upstream pseudoknot domain within the TMV 3' untranslated region. Polyclonal antibodies raised against wheat p102 were used to demonstrate that p102 is widely conserved in plant species. Moreover, specific RNA binding activity was detected in all plant species tested. Addition of anti-p102 antibodies to an in vitro translation lysate derived from wheat germ repressed translation, which was subsequently reversed by supplementing the lysate with p102. These findings suggest that this protein may play an important role in determining translational efficiency in plants.