The targeting of mRNA and local protein synthesis is important for the generation and maintenance of cell polarity. As part of the translational machinery as well as an actin/ microtubule-binding protein, elongation factor 1␣ (EF1␣) is a candidate linker between the protein translation apparatus and the cytoskeleton. We demonstrate in this work that EF1␣ colocalizes with ␤-actin mRNA and F-actin in protrusions of chicken embryo fibroblasts and binds directly to F-actin and ␤-actin mRNA simultaneously in vitro in actin cosedimentation and enzyme-linked immunosorbent assays. To investigate the role of EF1␣ in mRNA targeting, we mapped the two actin-binding sites on EF1␣ at high resolution and defined one site at the N-terminal 49 residues of domain I and the other at the C-terminal 54 residues of domain III. In vitro actin-binding assays and localization in vivo of recombinant full-length EF1␣ and its various truncates demonstrated that the C terminus of domain III was the dominant actin-binding site both in vitro and in vivo. We propose that the EF1␣-F-actin complex is the scaffold that is important for ␤-actin mRNA anchoring. Disruption of this complex would lead to delocalization of the mRNA. This hypothesis was tested by using two dominant negative polypeptides: the actin-binding domain III of EF1␣ and the EF1␣-binding site of yeast Bni1p, a protein that inhibits EF1␣ binding to F-actin and also is required for yeast mRNA localization. We demonstrate that either domain III of EF1␣ or the EF1␣-binding site of Bni1p inhibits EF1␣ binding to ␤-actin mRNA in vitro and causes delocalization of ␤-actin mRNA in chicken embryo fibroblasts. Taken together, these results implicate EF1␣ in the anchoring of ␤-actin mRNA to the protrusion in crawling cells.

In limited-stage DLBCL, the addition of rituximab to three cycles of CHOP plus IFRT met prespecified study criteria of efficacy, with 2-year PFS of at least 84%, meriting further investigation. There is a pattern of continuing relapse with modest survival gains. We hypothesize that such a pattern may be the result of biologic differences between limited- and advanced-stage lymphoma.