Figure 17.13. Model for a possible mechanism of mRNA masking ("structural masking theory"; A.S. Spirin, Mol. Reprod. Dev. 38, 107-117, 1994). The eukaryotic mRNA is complexed with a large amount of protein, thus forming mRNPs (or "informosomes"; A.S. Spirin, Curr. Topics Dev. Biol. 1, 1-38, 1996; Eur. J. Biochem. 10, 20-35, 1969). Binding of a masking protein to a defined section ("masking box", see Fig. 17.12) within the 3'-UTR may induce a structural rearrangement of the mRNP particle into a condensed form that may be inaccessible to initiation factors, ribosomes, ribonucleases, and poly(A) polymerase (masked mRNP). The sequence of events may vary in different situations; for example, first a masking protein is bound to a nascent mRNA chain and then the loading of a large number of core proteins result in a compact packing of the mRNP.

(Reproduced from A.S. Spirin, in "Translational Control", J.W.B. Hershey, M.B. Mathews & N. Sonenberg, eds., p.p. 319-334, CSHL Press, 1996).

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