Studying the Structural Organization of Polyribosomes with Alexander S. Spirin

---

Bruno P. Klaholz^1,2,3,4

¹Centre for Integrative Biology (CBI), Department of Integrated Structural Biology, IGBMC (Institute of Genetics and of Molecular and Cellular Biology), 67404 Illkirch, France

²Centre National de la Recherche Scientifique (CNRS) UMR 7104, 67404 Illkirch, France

³Institut National de la Santé et de la Recherche Médicale (INSERM) U964, 67404 Illkirch, France

⁴Université de Strasbourg, 67081 Strasbourg, France

Received May 20, 2021; Revised May 20, 2021; Accepted June 6, 2021

---

“Would it be possible to analyze molecular mechanisms and structural organisation of polyribosome assemblies using cryo electron tomography?” – we asked through a longstanding collaboration between my research group and that of Alexander S. Spirin. Indeed, it was: we found that double-row polyribosomes can have both circular and linear arrangements of their mRNA [Afonina, Z. A., et al. (2013) Biochemistry (Moscow)], we figured out how eukaryotic ribosomes assemble on an mRNA to form supramolecular left-handed helices [Myasnikov, A. G., et al. (2014) Nat. Commun.], that the circularization of polyribosomes is poly-A and cap-independent [Afonina, Z. A., et al. (2014) Nucleic Acids Res.], and that intermediary polyribosomes with open structures exist after a transition from a juvenile phase to strongly translating polysomes of medium size [Afonina, Z. A., et al. (2015) Nucleic Acids Res.] until they form densely packed helical structures with reduced activity. Our joint fruitful exchanges, hence, led to major advances in the field, which are reviewed here from a personal and historical perspective in memory of Alexander S. Spirin.

---

KEY WORDS: polyribosomes, polysomes, eukaryotic ribosomes, cryo electron microscopy, cryo electron tomography

DOI: 10.1134/S0006297921090030

---