Eukaryotic pre-mRNA is processed by a large multiprotein cleavage and polyadenylation complex to accurately cleave the 3’ end, and to catalyze the addition of the poly(A) tail. Within the cleavage and polyadenylation specificity factor (CPSF) machinery, the CPSF73 endonuclease subunit directly contacts both CPSF100 and the scaffold protein Symplekin to form a stable subcomplex known also as the core cleavage complex (CCC) or mammalian cleavage factor (mCF). Here we have taken advantage of a stable CPSF73-CPSF100 minimal complex fromE. cuniculito determine the solution structure of the folded complex formed by the first and second C-terminal domain (CTD1 and CTD2) of both proteins. We find a large number of contacts between both proteins in the complex, and notably in the region between CTD1 and CTD2. A previously unreported similarity is also evident between CTD2 and the TATA-box binding protein (TBP) domains. Separately, we have determined the structure of the terminal CTD3 domain of CPSF73, which also belongs to the TBP domain family and is connected by a flexible linker to the rest of CPSF73. Biochemical assays demonstrate a key role for the CTD3 of CPSF73 in the recognition of Symplekin, and structural models of the trimeric complex from other species allow for comparative analysis and support an overall conserved architecture.

Translation initiation in eukaryotes is an early step in protein synthesis, requiring multiple factors to recruit the ribosomal small subunit to the mRNA 5' untranslated region. One such protein factor is the eukaryotic translation initiation factor 4B (eIF4B), which increases the activity of the eIF4A RNA helicase, and is linked to cell survival and proliferation. We report here the protein backbone chemical shift assignments corresponding to the C-terminal 279 residues of human eIF4B. Analysis of the chemical shift values identi es one main helical region in the area previously linked to RNA binding, and con rms that the overall C-terminal region is intrinsically disordered. Biological contextAt its core, translation initiation in eukaryotes involves recruitment of the small ribosomal subunit with associated protein factors (the 43S pre-initiation complex) onto the protein-coding mRNA (Jackson et al. 2010). This process is usually achieved by the help of a mRNA cap-binding complex known as eukaryotic translation initiation factor 4F (eIF4F; comprising the three factors eIF4E, eIF4A and eIF4G), as well as eIF4B (or the homologue eIF4H) (Merrick 2015). In a concerted action, these factors recognize the mRNA 5'-cap and unwind the structured elements at the 5'-end untranslated region (5'-UTR) of the mRNA. This action facilitates the recruitment of the 43S pre-initiation complex, the scanning of the mRNA towards the start-codon recognition, and also ribosome assembly (Jackson et al. 2010). Throughout this process,

Translation initiation in eukaryotes is an early step in protein synthesis, requiring multiple factors to recruit the ribosomal small subunit to the mRNA 5’ untranslated region. One such protein factor is the eukaryotic translation initiation factor 4B (eIF4B), which increases the activity of the eIF4A RNA helicase, and is linked to cell survival and proliferation. We report here the protein backbone chemical shift assignments corresponding to the C-terminal 279 residues of human eIF4B. Analysis of the chemical shift values identifies one main helical region in the area previously linked to RNA binding, and confirms that the overall C-terminal region is intrinsically disordered.