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. 2019 Apr 19;116(19):9340–9349. doi: 10.1073/pnas.1901742116

Fig. 6.

Fig. 6.

Model for p180-SF3b4-cis-element-dependent polyribosome assembly that facilitates efficient translation. (A) An mRNA containing the cis-element in its 5′ UTR is targeted to p180 on the ER via the bridging factor SF3b4 mediated by Ct domain of p180. p180-SF3b4 interaction facilitates the assembly of heavy polyribosomes that confer high-rate protein synthesis. Either a SRP-dependent pathway (a-1) or a SRP-independent pathway (a-2) is the targeting route for mRNAs toward the ER. (B) In the presence of the cytoplasmic Ct fragment, mRNA containing the cis-element does not interact with p180, thereby preventing heavy polyribosome formation. (C) The translational efficiency of mRNAs devoid of the 5′ UTR cis-element remains constant irrespective of manipulation of SF3b4 or p180.