Immunoprecipitation using a flag-monoclonal antibody followed by western blot analysis of the precipitates with a myc-monoclonal antibody clearly demonstrates co-immunoprecipitation of myc-eEF1 with flag-RPB3 (fig. and general transcription factors to form the holoenzyme complex[1]-[4]. We had previously cloned two subunits of the human pol II enzyme, RPB11 (UniProtKB:P52435) and RPB3 (UniProtKB:P19387)[5][6]. RPB3 and RPB11 form a heterodimer that is reminiscent of the subunit homodimer of bacterial RNA polymerase that is involved in promoter acknowledgement. The RPB3/RPB11 heterodimer plays a central role in the conversation between pol II and the mediator complex, suggesting functional conservation from prokaryotes to eukaryotes[7]. Using the RPB3 subunit as bait in a series of yeast two-hybrid experiments, we defined RPB3 involvement in tissue-specific transcription. We exhibited that RPB3 directly contacts several transcription factors, including ATF4, a member of the ATF/CREB family and Myogenin, a member of the MyoD gene family[8][9]. In addition, we have recently shown that RPB3 is usually retained/stored in the cytoplasm interacting with CCHCR1, the psoriasis vulgaris candidate gene product[10]. Here, we show, for the first time, that RPB3, alone and complexed in pol II, interacts with the Eukaryotic Elongation Factor 1 subunit gamma (eEF1) (UniProtKB:P26641) that is a a part of eEF1 complex. Eukaryotic elongation factor 1 (eEF1) is usually a macromolecular complex that catalyses the transfer of aminoacyl-tRNAs to ribosomes[11]. In higher eukaryotes, eEF1 consists of three or four subunits, eEF1, eEF1, eEF1 and eEF1, respectively renamed eEF1A, eEF1B, eEF1B and eEF1B[11][12]. For the purposes of simplicity in this article we use the older nomenclature (eEF1). The eEF1 subunit of EF1 binds aminoacyl-tRNA in a GTP-dependent manner and the producing ternary complex binds to the ribosome[13]. Following aminoacyl-tRNA binding to the ribosomal A site via a codon-anticodon conversation, GTP is usually OXF BD 02 hydrolysed to GDP. Subsequently, GDP remains bound to eEF1 and eEF1 functions as nucleotide exchange factor, regenerating eEF1-GTP for the successive elongation cycle. The physiological role of the eEF1 subunit in this context is still not well defined. There is some evidence that eEF1 stimulates, but is not required for, the nucleotide exchange activity of eEF1[12]. Indeed, eEF1 appears dispensable for translation, its absence doesn’t seem to impact global rate of translational elongation. Instead eEF1 depletion inSaccharomyces cerevisiaeprovides resistance to oxidative stress[14]. A role of eEF1 in the oxidative stress response pathways is usually justified by the presence in the N terminus of eEF1 of a conserved sequence resembling the glutathione-binding region of the theta class of Glutathione S-transferases OXF BD 02 (GST) enzymes, which is usually involved in the detoxification of oxygen radicals[15]. The over-expression of eEF1, explained in several tumours, influences tumour aggressiveness presumably by altering the redox balance[12],[16]. Nevertheless, multiple/additional functions for eEF1 are emerging, some of which can be regulated by phosphorylation driven by several protein kinases[17][18]. eEF1 displays an affinity GNGT1 for membrane and cytoskeleton elements and it could properly anchor the different subunits of the EF1 complex to the cytoskeleton[12],[19][21]. Interestingly, Al-Maghrebi et al. (2002) showed in studies in vitro and in vivo that eEF1 binds the 3UTR of Vimentin (UniProtKB:P08670) mRNA, demonstrating for the first time the RNA-binding properties of eEF1[22]. In addition, human eEF1 was recently recognized in a proteomic screen as a member of the pre-mRNA 3 end cleavage complex[23]. To further reinforce a role for eEF1 in RNA metabolism, Fan et al. exhibited in Drosophila that eEF1 activity is required for the viability of both the whole animal and individual cells, emphasising that recessive lethality occurs during early larval development. This observation is usually consistent with an extensive maternal contribution of the RNA and protein to the embryo[18]. In this scenario eEF1 could contribute to the OXF BD 02 anchoring and translation of a set of mRNAs that are preferentially translated on cytoskeletal- or membrane-bound ribosomes, such as Vimentin mRNA. Vimentin is the major intermediate filament protein involved in cell structural support, transmission transduction and organelle positioning[24]. Morris et al. (2000) exhibited that misdirecting Vimentin mRNA it is possible to alter cell morphology.