Identification and characterization of functionally critical, conserved motifs in the internal repeats and N-terminal domain of yeast translation initiation factor 4B (yeIF4B) [Gene Regulation]

November 27th, 2013 by Zhou, F., Walker, S. E., Mitchell, S. F., Lorsch, J. R., Hinnebusch, A. G.

eIF4B has been implicated in attachment of the 43S preinitiation complex (PIC) to mRNAs and scanning to the start codon. We recently determined that the internal 7 repeats (of ~26 amino acids each) of S. cerevisiae eIF4B (yeIF4B) comprise the region most critically required to enhance mRNA recruitment by 43S PICs in vitro and stimulate general translation initiation in yeast. Moreover, whereas the N-terminal domain (NTD) of yeIF4B contributes to these activities, the RNA recognition motif (RRM) is dispensable. We have now determined that only 2 of the 7 internal repeats are sufficient for wild-type (WT) yeIF4B function in vivo when all other domains are intact. However, three or more repeats are needed in the absence of the NTD or when the functions of eIF4F components are compromised. We corroborated these observations in the reconstituted system by demonstrating that yeIF4B variants with only one or two repeats display substantial activity in promoting mRNA recruitment by the PIC, whereas additional repeats are required at lower levels of eIF4A or when the NTD is missing. These findings indicate functional overlap among the 7-repeat and NTD domains of yeIF4B and eIF4A in mRNA recruitment. Interestingly, only three highly conserved positions in the 26-aa repeat are essential for function in vitro and in vivo. Finally, we identified conserved motifs in the NTD and demonstrate functional overlap of two such motifs. These results provide a comprehensive description of the critical sequence elements in yeIF4B that support eIF4F function in mRNA recruitment by the PIC.
  • Posted in Journal of Biological Chemistry, Publications
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