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Nucleic Acids Res. 2015 Jan;43(1):618-28. doi: 10.1093/nar/gku1270. Epub 2014 Dec 17.

Conformation transitions of eukaryotic polyribosomes during multi-round translation.

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Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia.
Centre for Integrative Biology (CBI), Department of Integrated Structural Biology, IGBMC (Institute of Genetics and of Molecular and Cellular Biology), Centre National de la Recherche Scientifique (CNRS) UMR 7104; Institut National de la Santé de la Recherche Médicale (INSERM) U964; Université de Strasbourg, 1 rue Laurent Fries, 67404 Illkirch, France.
Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia


Using sedimentation and cryo electron tomography techniques, the conformations of eukaryotic polyribosomes formed in a long-term cell-free translation system were analyzed over all the active system lifetime (20-30 translation rounds during 6-8 h in wheat germ extract at 25°C). Three distinct types of the conformations were observed: (i) circular polyribosomes, varying from ring-shaped forms to circles collapsed into double rows, (ii) linear polyribosomes, tending to acquire planar zigzag-like forms and (iii) densely packed 3D helices. At the start, during the first two rounds of translation mostly the circular (ring-shaped and double-row) polyribosomes and the linear (free-shaped and zigzag-like) polyribosomes were formed ('juvenile phase'). The progressive loading of the polyribosomes with translating ribosomes induced the opening of the circular polyribosomes and the transformation of a major part of the linear polyribosomes into the dense 3D helices ('transitional phase'). After 2 h from the beginning (about 8-10 rounds of translation) this compact form of polyribosomes became predominant, whereas the circular and linear polyribosome fractions together contained less than half of polysomal ribosomes ('steady-state phase'). The latter proportions did not change for several hours. Functional tests showed a reduced translational activity in the fraction of the 3D helical polyribosomes.

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