Distance between adjacent ribosomes on polysome (exit tunnel to entrance tunnel)

Value 7 nm Range: ±1 nm
Organism Bacteria Escherichia coli
Reference Brandt F, Etchells SA, Ortiz JO, Elcock AH, Hartl FU, Baumeister W. The native 3D organization of bacterial polysomes. Cell. 2009 Jan 23 136(2):261-71. p.266 right column 2nd paragraphPubMed ID19167328
Method Researchers employed cryoelectron tomography and a template-matching approach to map 70S ribosomes in vitrified bacterial translation extracts and in lysates of active E. coli spheroplasts. The spatial orientation of ribosomes in polysomes was determined by 3D template matching with a resolution-adjusted density derived from a 70S ribosome reference structure (Schuwirth et al., 2005). Particle coordinates and orientations in relation to the reference (Figure S3) were extracted from peaks in the resulting 3D crosscorrelation function (see Experimental Procedures). The distance between codon recognition sites in densely packed neighboring ribosomes was estimated as follows. Positions of 26 nucleotides resolved in a 70S ribosomal crystal structure containing mRNA (Yusupova et al., 2006) were used in the polysomal model for each ribosome. Between two adjacent ribosomes, an average distance of 7 ± 1 nm was determined from the exit site of the mRNA of one ribosome to the entrance site of the next ribosome.
Comments Researchers' analysis reveals a remarkably well defined arrangement of ribosomes in staggered or helical orientations, with the mRNA being sequestered on the inside, while the tRNA entrance sites and the polypeptide exit sites are exposed to the cytosol. For the transcripts Luc 197, 371, and 550, (numbers of amino acids, multiply by 3 to receive nucleotide number) the average numbers of ribosomes within putative polysomes were 4±1, 8±2, and 11±2, respectively. These transcripts were constructed in vitro. For number of ribosomes in polysome in vivo see BNID 105207, 102024. See BNID 105000. Note-a measured value of 7.35nm given in supporting online material p.6
Entered by Uri M
ID 105001