A helical polysome model

Pfuderer, Peter; Cammarano, Piero; Holladay, Daniel R.; Novelli, G. David

doi:10.1016/0926-6585(65)90186-x

Cited by 47 publications

(11 citation statements)

References 21 publications

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“…Our results, in fact, appear consistent with those of early studies using purified polysomes devoid of protein factors. Pfuderer et al first proposed a helical model of polysomes based on a hydrodynamic analysis [27], and Shelton et al suggested from their EM observations the possibility that polysomal mRNA has a natural tendency to bend [10]. Recently Christensen et al provided EM results further supporting this notion by showing the direction of the bend relative to ribosomal orientation on the mRNA [12].…”

Section: Resultsmentioning

confidence: 99%

Formation of circular polyribosomes in wheat germ cell‐free protein synthesis system

et al. 2004

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We report a morphological study of functioning ribosomes in a e⁄cient and robust cell-free protein synthesis system prepared from wheat embryos. Sucrose density gradient analysis of translated mixtures programmed with luciferase mRNAs having di¡erent 5P P and 3P P untranslated regions showed formation of large polysomes. Electron microscopic examination of translation mixtures programmed with those of capped and polyadenylated mRNA revealed that ribosomes assemble into a circular-type polysome in vitro. Furthermore, a series of experiments using mRNAs lacking either cap, poly(A) tail or both also resulted in the formation of circular polysomes, which are indistinguishable from those with the original mRNA. The wheat germ cell-free system may provide a good experimental system for understanding functional ribosomes at the molecular level. ß 2004 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

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Section: Resultsmentioning

confidence: 99%

Formation of circular polyribosomes in wheat germ cell‐free protein synthesis system

et al. 2004

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“…The tubes were fractionated into 30-35 fractions by aspiration from the base of the tube through a Pasteur pipette using a peristaltic pump. It was calculated that particles of sedimentation characteristic greater than 375S (equivalent to a polysome made up from 13 ribosomal units [3] ) would have pelleted under these conditions. The table excludes consideration of all a4C-material sedimenting so slowly as not to enter the top of the gradient (20% sucrose).…”

Section: °C (Tags)mentioning

confidence: 99%

Membrane—ribosome interactions: Artefacts resulting from the temperature‐dependent formation of ribosomal aggregates

1975

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“…3), and the measured values, especially in the angular range b < 0.01 nm-l, these models are also unlikely. A helix with four ribosomes per turn [9] shows the correct parameters; however, the calculated interaction term reveals significant deviations from the experimental values (Fig.3). The best correspondence, both of the parameters and of the interaction terms, can be obtained for models 3 and 7, which are spatially very compact (Table 1).…”

Section: Discussionmentioning

confidence: 98%

Studies on the Structure of Rat-Liver Polysomes by Small-Angle X-Ray Scattering

1978

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The spatial structure of rat liver polysomes in dilute solution has been studied by the small-angle X-ray scattering technique. The distance between the mass centres of neighbouring ribosomes on the mRNA molecule is 35 nm, and the distance from next-but-one neighbour, about 55 nm. The spatial arrangement of the ribosomes on the polysome is compact; stretched configurations can be ruled out, The best model is a solenoid with six ribosomes per turn and a pitch of about 33 nm. The greatest diameter of a polysome with eight ribosomes is 130 nm, the radius of gyration 34 nm.As electron micrographs [l -61 and sedimentation data [7-101 have shown, polysomes build up specific spatial structures. Two characteristics of this structure are apparently connected with the function of the polysomes: (a) the distribution of the ribosomes along the mRNA, and (b) the spatial organization of the ribosome . mRNA complex. Biochemical results [l 11 lend support to the conclusion that the ribosomes are uniformly distributed along the mRNA under normal conditions. About 90 nucleotides belong to one ribosome in liver polysomes and the gaps between the ribosomes contain about 30 nucleotides [ l l , 121. On the other hand, investigations by Talkad et al. [13] on the rate of translation of the mRNA in Escherichia coli have led to a model with a stuttering movement of the ribosomes, resulting in different spacings between the ribosomes on the mRNA. Changes of the rate of protein synthesis in the liver, for example in different dietary situations, are connected with variations in the profiles of polysomes. These variations may be due to different spacings between the ribosomes on the mRNA [14]. The number of nucleotides, however, cannot be interpreted as a geometrical distance of the ribosomes since the mRNA molecule can build up secondary or tertiary structures [15,16].The analysis of polysome suspensions by smallangle X-ray scattering enables conclusions about the organization of polysomes and distances between the ribosomes on the mRNA.In contrast to the many small-angle X-ray and neutron scattering experiments of isolated ribosomes [17-21 1, no studies of polysomes have yet been carried out in dilute solutions. The advantage of examining solutions by scattering methods compared with electron microscopic measurements is that the formation of artefacts during preparation [3,4] is reduced and that the complicated spatial structure is not projected to a plane [4]. On the other hand, the finding of a structure model by means of scattering methods requires time-consuming 'trial and error' methods. Structure proposals based on electron microscopy may be used to shorten this 'trial and error' procedure considerably. MATERIALS AND METHODS Preparation of Ribosomes and PolysomesLivers from Wistar rats, starved for 18 h, were homogenized in buffer A (SO mM Tris-HC1, 25 niM KC1,S mM MgC12,S mM 2-mercaptoethanol, pH 7.5) containing 250 mM sucrose for 30 s at 0 "C (weight/ volume ratio 1 : 2). The homogenate was centrifuged twice at 10000 x g for 10 mi...

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A helical polysome model

Cited by 47 publications

References 21 publications

Formation of circular polyribosomes in wheat germ cell‐free protein synthesis system

Formation of circular polyribosomes in wheat germ cell‐free protein synthesis system

Membrane—ribosome interactions: Artefacts resulting from the temperature‐dependent formation of ribosomal aggregates

Studies on the Structure of Rat-Liver Polysomes by Small-Angle X-Ray Scattering

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