Suppose that a bicistronic mRNA is being translated and that the first gene is preceded by a 5' cap while the second is preceded by an internal ribosome entry site (IRES). If a ribosome begins translating the first gene after 5' cap recognition, will it continue through the IRES to translate the second gene? Or will it be stalled, or even dissociated upon encountering the IRES?
Hey David,
When we design a bicistronic construct we will incorporate stop codon for the first cistron followed by an IRES and start codon for second cistron, in that order. So theoretically, when the ribosome reaches stop codon for first cistron it should dissociate. And, the second cistron can only translate if the ribosome is recruited directly to IRES.
But, if there is no stop codon between first cistron and IRES, I think the ribosome translating the first cistron will halt when it reaches the weird secondary or even tertiary structure of IRES and induce Nonsense mediated mRNA decay.
I hope this was helpful.
Cheers!
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