No abstract

No abstract

No abstract

The ribosome uses tRNAs to translate the genetic information into the amino acid sequence of proteins. The mass ratio of a tRNA to the ribosome is in the order of 1:100; because of this unfavorable value it was not possible until now to determine the location of tRNAs within the ribosome by neutron-scattering techniques. However, the new technique of proton-spin contrast-variation improves the signal-to-noise ratio by more than one order of magnitude, thus enabling the direct determination of protonated tRNAs within a deuterated ribosome for the first time. Here we analyze a pair of ribosomal complexes being either in the preor post-translocational states that represent the main states of the elongating ribosome. Both complexes were derived from one preparation. The orientation of both tRNAs within the ribosome and their mutual arrangement are determined by using an electron microscopy model for the Escherichia coli ribosome and the tRNA structure. The mass center of gravity of the (tRNA) 2 mRNA complex moves within the ribosome by 12 ؎ 4 Å in the course of translocation as previously reported. The main results of the present analysis are that the mutual arrangement of the two tRNAs does not change on translocation and that the angle between them is, depending on the model used, 110°؎ 10°before and after translocation. The translocational movement of the constant tRNA complex within the ribosome can be described as a displacement toward the head of the 30S subunit combined with a rotational movement by about 18°.The central machinery of the translational apparatus is the ribosome, which is one of the most complicated cellular structures. It separates into two subunits and consists of more than 50 components. The central RNA ligands of the ribosome during protein synthesis are tRNAs and mRNA. mRNA brings the genetic information to the ribosome where tRNAs are used to interpret the codon sequence of the mRNA in terms of an amino acid sequence in the growing peptide (for a recent synopsis see ref. 1). Data derived from cross-linking studies, chemical protection, and fluorescence measurements have led to the proposal of conflicting models for the tRNA positions in the elongating ribosome (2-4) because of uncertainties in the spatial assignment of ribosomal components. Thus, additional information on the location of tRNAs by using direct physical methods is necessary to evaluate and refine the models. Positions of tRNAs within the ribosome deduced from electron microscopy (EM) have been proposed recently (5, 6). Neutron-scattering analysis has been applied for direct localization of the mass center of gravity for the (tRNA) 2 mRNA complex present on the ribosome during elongation (7).Here we describe the relative arrangement of the tRNAs before and after translocation as derived from the neutronscattering data. The mutual arrangement of the tRNAs does not change on translocation from their pre-to their posttranslocational positions, and the angle between them remains constant at 110°Ϯ 10°. MATERIALS AND METHO...

No abstract