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A polyribosome (or polysome) is a complex of an mRNA molecule is translated by two or more ribosomes to form polypeptide chains during active translation, this process is called translatome.^[1][5] Originally coined "ergosomes" in 1963 ^[2] they were further characterized by Jonathan Warner, Paul Knopf, and Alex Rich.^[3] The study of translatome and polysome analysis would lead to a better insight of the complexity of the regulatory pathway; how mutations, extracellular stimuli, intercellular cues, growth conditions, and stress could lead to the change of translation in the cell, and which specific components would accompany to the translator machinery^{[5] [6] [7]}. Ribosomes play a key role in the synthesis of polysome, they act as a platform for signaling molecules to get involved in the diverse modification from the emergence of polypeptides and ribosomes; also they aid the nascent polypeptides to fold with the presence of chaperones, later on would impact on the function of synthesized polysome^[7].

Structure

Polysomes can be directly visualized by electron microsopy because they form very high molecular weight particles.^[1] Many ribosomes simultaneously read one mRNA progressing along the mRNA to synthesize the same protein. They may appear as linear polysomes or circular rosettes with microscopy but are mainly circular in vivo. This circularization is aided by the fact that mRNA is able to be twisted into a circular formation, creating a cycle of rapid ribosome recycling and utilization of ribosomes. The 5' 7-methylguanosine cap and 3' poly(A) tail present on eukaryotic mRNA aid in this process.^[4]

Types of Polysome

Polyribosomes can be found in three forms: free, cytoskeletal bound, and membrane bound. The three forms are detached by the difference of their poly(A) and non-poly(A) protein binding sequence from MPC-11 and Krebs II ascites cells using the procedure of detergent and salt extraction^[8].

References

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^{a b} Michael M. Cox; Jennifer A. Doudna; Michael O'Donnell (July 2011). Molecular Biology: Principles and Practice. Macmillan Higher Education. ISBN 978-1-4292-9273-3.

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^ Staehelin, T.; Brinton, C. C.; Wettstein, F. O.; Noll, H. (1963). "Structure and Function of E. Coli Ergosomes". Nature. 199 (4896): 865–870. doi:10.1038/199865a0. ISSN 0028-0836.

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^ Warner JR, Knopf PM, Rich A (1963). "A multiple ribosomal structure in protein synthesis". Proc. Natl. Acad. Sci. U.S.A. 49: 122–129. Bibcode:1963PNAS...49..122W. doi:10.1073/pnas.49.1.122. PMC 300639. PMID 13998950. Summary

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^ Harvey Lodish (1999). "4.5. Stepwise Formation of Proteins on Ribosomes". Molecular cell biology. New York: Scientific American Books. ISBN 0-7167-3136-3.

5 Brielle, Régine; Pinel-Marie, Marie-Laure; Chat, Sophie; Gillet, Reynald; Felden, Brice. "Purification, identification, and functional analysis of polysomes from the human pathogen Staphylococcus aureus". Methods. doi:10.1016/j.ymeth.2016.10.003.

6  Qin, Daoming; Fredrick, Kurt. "Chapter Eight - Analysis of Polysomes from Bacteria". Methods in Enzymology. Academic Press. pp. 159–172.

7 Gandin, Valentina; Sikström, Kristina; Alain, Tommy; Morita, Masahiro; McLaughlan, Shannon; Larsson, Ola; Topisirovic, Ivan (17 May 2014). "Polysome Fractionation and Analysis of Mammalian Translatomes on a Genome-wide Scale". Journal of Visualized Experiments : JoVE (87). doi:10.3791/51455. ISSN 1940-087X. PMID 8035778.

8 Moss, R.; Pryme, I. F.; Vedeler, A. (23 February 1994). "Free, cytoskeletal-bound and membrane-bound polysomes isolated from MPC-11 and Krebs II ascites cells differ in their complement of poly(A) binding proteins". Molecular and Cellular Biochemistry. 131 (2): 131–139. ISSN 0300-8177. PMID 8035778.