title: Formation of 70S ribosomes: large activation energy is required for the adaptation of exclusively the small ribosomal subunit.
abstract: Association of ribosomal subunits is an essential reaction during the initiation phase of protein synthesis. Optimal conditions for 70S formation in vitro were determined to 20 mM Mg2+ and 30 mM K+. Under these conditions, the association reaction proceeds with first order kinetics, suggesting a conformational change to be the rate-limiting step. 70S formation separates into two sub-reactions, the adaptation of the ribosomal subunits to the association conditions and the association step itself. The activation energy of the process was determined to 78 kJ/mol and revealed to be required exclusively for the adaptation of the small subunit, rather than the large subunit or the association step. The presence of mRNA [poly(U)] together with cognate AcPhe-tRNA, accelerates the association rate significantly, forming a well-defined 70S peak in sucrose gradient profiles. mRNA alone provokes an equivalent acceleration, however, the resulting 70S couple impresses as an ill-defined, broad peak, probably indicating the readiness of the ribosome for tRNA binding, upon which the ribosome flips into a defined state.
authors.affiliation: Max-Planck-Institut für Molekulare Genetik, Berlin, Germany.
authors.forename: Gregor
authors.initials: G
authors.lastname: Blaha
authors.forename: Nils
authors.initials: N
authors.lastname: Burkhardt
authors.forename: Knud H
authors.initials: KH
authors.lastname: Nierhaus
mesh_terms: D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009690:Nucleic Acid Conformation; D011072:Poly U / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D012360:RNA, Transfer, Phe / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D012333:RNA, Messenger; D012346:RNA, Transfer, Amino Acyl; D012360:RNA, Transfer, Phe; D011072:Poly U; D008274:Magnesium; D011188:Potassium