Figure 7-106. A model for nonsense-mediated mRNA decay.

Figure 7-106A model for nonsense-mediated mRNA decay

According to this model, nuclear proteins (orange) mark the exon-exon boundaries on a spliced mRNA molecule. These proteins are thought to assemble in concert with the splicing reaction and may also be involved in the transport of mature mRNAs from the nucleus (see Figure 6-40). A mature mRNA molecule is exported from the nucleus but remains in the vicinity of the nuclear envelope where a “test” round of translation is performed by the ribosome (green) aided by additional surveillance proteins (dark green). If an in-frame stop codon is encountered before the final exon-exon boundary is reached, the mRNA is subject to nonsense-mediated decay. If not, the mRNA is released from the nuclear envelope (perhaps because of a displacement of the exon-exon marking proteins by the ribosome) and is free to undergo multiple rounds of translation in the cytosol. According to the model shown, the test round of translation occurs just outside the nucleus; however, it is also possible that it takes place within the nucleus, just before the mRNA is exported. (Adapted from J. Lykke-Anderson et al., Cell 103:1121–1131, 2000.)

From: Posttranscriptional Controls

Cover of Molecular Biology of the Cell
Molecular Biology of the Cell. 4th edition.
Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002.
Copyright © 2002, Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter; Copyright © 1983, 1989, 1994, Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson .

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