The KH-Domain Protein αCP Has a Direct Role in mRNA Stabilization Independent of Its Cognate Binding Site

Abstract

Previous studies suggest that high-level stability of a subset of mammalian mRNAs is linked to a C-rich motif in the 3′ untranslated region (3′UTR). High-level expression of human α-globin mRNA (hα-globin mRNA) in erythroid cells has been specifically attributed to formation of an RNA-protein complex comprised of a 3′UTR C-rich motif and an associated 39-kDa poly(C) binding protein, αCP. Documentation of this RNA-protein α-complex has been limited to in vitro binding studies, and its impact has been monitored by alterations in steady-state mRNA. Here we demonstrate that αCP is stably bound to hα-globin mRNA in vivo, that α-complex assembly on the hα-globin mRNA is restricted to the 3′UTR C-rich motif, and that α-complex assembly extends the physical half-life of hα-globin mRNA selectively in erythroid cells. Significantly, these studies also reveal that an artificially tethered αCP has the same mRNA-stabilizing activity as the native α-complex. These data demonstrate a unique contribution of the α-complex to hα-globin mRNA stability and support a model in which the sole function of the C-rich motif is to selectively tether αCP to a subset of mRNAs. Once bound, αCP appears to be fully sufficient to trigger downstream events in the stabilization pathway.