ETD Collection

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    Biophysical characterisation of human eukaryotic elongation factor 1 Beta and its interaction with human eukaryotic elongation factor 1 Gamma
    (2017) Elebo, Nnenna Chioma
    Eukaryotic protein synthesis occurs in three phases: initiation, elongation and termination. The elongation phase is mediated by elongation factors. Elongation factors are divided into elongation factor 1 (eEF1) and elongation factor 2 (eEF2). Elongation factor 1 complex are proteins that mediates the extension of growing polypeptide chains by adding one amino acid residue at a time. The eEF-1 complex comprises of four subunits, eEF1α, eEF1β, eEF1γ and eEF1δ. The β-subunit of elongation factor 1 complex (eEF1) plays a central role in the elongation step of eukaryotic protein biosynthesis, which essentially involves interaction with the α-subunits (eEF1α) and γ-subunits (eEF1γ). To biophysically characterise heEF1β, three E. coli expression vector systems was constructed for recombinant expression of the full length (FL-heEF1β), amino terminus (NT-heEF1β) and the carboxyl terminus (CT-heEF1β) regions of the protein. NT-heEF1β was created from the FL-heEF1β by site-directed mutagenesis using mutagenic forward and reverse primers. The results suggest that heEF1β is predominantly alpha-helical and possesses an accessible hydrophobic cavity in the CT-heEF1β. Both FL-heEF1β and NT-heEF1β forms dimers of size 62 kDa and 30 kDa, respectively, but the CT-heEF1β is monomeric. FL-heEF1β interacts with the N-terminus GST-like domain of heEF1γ (NT-heEF1γ) to form a 195 kDa complex, or a 230 kDa complex in the presence of oxidised glutathione. On the other hand, NT-heEF1β forms a 170 kDa complex with NT-heEF1γ and a high molecular weight aggregate of size greater than 670 kDa. This study affirms that the interaction between heEF1β and heEF1γ subunits occurs at the N-terminus regions of both proteins, also the N-terminus region of heEF1β is responsible for its dimerisation and the C-terminus region of heEF1β controls the formation of an ordered eEF1β-γ oligomer, a structure that may be essential in the elongation step of eukaryotic protein biosynthesis.
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    Protein synthesis, cell division and cell death
    (1993) Davidoff, Avri Nava
    In this study the morphologic, cytokinetic, biochemical, and molecu1w: consequences of low-dose continuous Puromycin-exposure were examined in HL-60 cells, and in a variety of malignant and non-malignant human and murine cell types. Puromycin (PM) is a composite of the amino nucleoside dimethyladenosine and tyrosine-o-methylether. Functionally it is an analogue of the terminal aminoacyl-adenosine portion of aminoacyl-tRNA, more specifically of tyrosyl..tRNA. At high concentrations 5-S0#tg/ml (10-100#tM) PM has been found to block protein synthesis completely by causing the premature release from the ribosomes of truncated peptide chains which are bound to PM through their carboxyl termini. The nascent PMGpeptide complexes (PMPs) are rapidly degraded through a ubiquitin-dependent pathway and are of interest because of (i) their potential to compete for degradation with the natural substrates of the ubiquitin-dependent pathway, including cyclin B, and (ii) because their structure predicts an inhibitory effect on tyrosine kinase activity. In the current' study then, special consideration was given to the effect of PM on the cell cycle, on apoptosis (programmed. cell death), and on tyrosine kinase activity, As a means of comparison, certain of these effects were also examined with respect to another translation inhibitor Cycloheximide (CHX), to two other substituted purines Puromycin Amino nucleoside (PAN) and 6..Dimethylaminopurine (6-DMAP), as well as to the cyclophospbamide derivative Mafosfamide (ASTA Z 7557).