title: Conformation transitions of eukaryotic polyribosomes during multi-round translation.
abstract: 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.
authors.affiliation: Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia.
authors.forename: Zhanna A
authors.initials: ZA
authors.lastname: Afonina
authors.affiliation: 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.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Myasnikov
authors.affiliation: Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Shirokov
authors.affiliation: 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.
authors.forename: Bruno P
authors.initials: BP
authors.lastname: Klaholz
authors.affiliation: Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia spirin@vega.protres.ru.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Spirin
mesh_terms: D002474:Cell-Free System; D020285:Cryoelectron Microscopy; D008958:Models, Molecular; D011132:Polyribosomes / Q000737:chemistry*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000737:chemistry
chemical_list: D012333:RNA, Messenger